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Kezhang Qin - One of the best experts on this subject based on the ideXlab platform.

  • thermal history of an early paleozoic Epithermal Deposit constraints from 40ar 39ar and u th he thermochronology at zhengguang eastern central asian orogenic belt
    Ore Geology Reviews, 2020
    Co-Authors: Le Wang, Kezhang Qin, Noreen J Evans, Mingjian Cao, Martin Danisik, Guoxue Song, Xuyong Pang
    Abstract:

    Abstract The Zhengguang Epithermal Au-Zn Deposit, located in Heilongjiang Province, NE China, is an Early Paleozoic intermediate sulfidation Epithermal Deposit which is adjacent to the Duobaoshan and Tongshan porphyry Cu Deposits in the Duobaoshan magmatic arc, eastern Central Asian Orogenic Belt (CAOB). Our new 40Ar/39Ar dating presents plateau ages of 276.9 ± 1.2 Ma (MSWD = 1.5) for adularia and 265.7 ± 1.2 Ma (MSWD = 3.5) for illite. These ages are clearly younger than the mineralization age of Zhengguang (~480 Ma) and therefore represent a post-ore event which reset the adularia and illite argon systems. The resetting event could be related to post-collision of Xing’an Block and Songliao-Xilinhot Block. The weighted mean of zircon (U–Th)/He ages (ZHe) and apatite (U–Th)/He ages (AHe) from the same dacite porphyry with illite dating sample are 192 ± 10 Ma (MSWD = 2.2) and 98.8 ± 5.3 Ma (MSWD = 2.1), respectively. The ZHe age (~190 Ma) indicates a tectonothermal resetting event, possibly related to the development of Tongshan fault whereas the AHe age (~100 Ma) likely reflects 3 km-deep burial at Zhengguang. The intra-sample variations of (U–Th)/He ages for zircon grains are mainly due to radiation damage, while those for apatite are unknown. We argue that the post-ore volcanic eruption and slow uplift and exhumation rate caused by rollback of the Paleo-Pacific plate could facilitate burial and preservation of the Epithermal (and by inference porphyry) Deposits in NE China. Considering the complex collisional and amalgamation history in this area, we believe that there is exploration potential for ancient porphyry and Epithermal Deposits within the eastern section of the CAOB.

  • geology and genesis of the early paleozoic zhengguang intermediate sulfidation Epithermal au zn Deposit northeast china
    Ore Geology Reviews, 2020
    Co-Authors: Kezhang Qin, Le Wang, Guoxue Song, Xuyong Pang, Xinyu Zou
    Abstract:

    Abstract Zhengguang is a partly eroded (about ≥500 m being eroded), structurally controlled intermediate sulfidation (IS) Epithermal gold-zinc Deposit, characterized by wide distribution of base metal sulfides, Fe-poor sphalerite and Mn-calcite, hosted by the Late Cambrian-Early Ordovician basaltic-andesitic volcanic and volcano-sedimentary rocks in northeast China. The Deposit is located 4 and 8 km from the Early Ordovician Tongshan (including several IS veins about ~500 m away in the east called East Tongshan) and Duobaoshan porphyry copper Deposits, respectively. A 484.8 ± 8.7 Ma (MSWD = 198) of Re-Os isochron age on pyrite indicates that it is the most ancient intermediate sulfidation Deposit that has been dated. Four stages of veins have been discerned at Zhengguang. Early magnetite ± chalcopyrite ± epidote ± chlorite and K-feldspar ± pyrite ± chalcopyrite veins (stage I) were associated with restricted K-feldspar ± epidote (locally with chlorite) alteration and propylitic (epidote ± chlorite ± calcite) assemblages. Two primary Epithermal gold stages developed at Zhengguang: pyrite-quartz ± Fe-poor sphalerite ± chalcopyrite ± galena ± electrum ± petzite ± hessite ± tetrahedrite/tennantite ± adularia veins (stage II) and (Mn-)calcite-quartz-pyrite ± Fe-poor sphalerite ± chalcopyrite ± galena ± hessite ± native gold (stage III), plus a late barren stage characterized by little sulfides (calcite ± chlorite ± hematite ± quartz, stage IV). Gold occurs chiefly as micro-inclusions of electrum and petzite in pyrite and sphalerite of stages II and III. Stable isotope analyses and fluid inclusion results indicate a magmatic-hydrothermal component in the ore fluids. Fluid inclusion data from stage I yielded the highest salinity (∼6.9 wt% NaCl) and homogenization temperature (average 264 °C). Calculated oxygen isotope composition of fluid (δ18Owater up to 4.9‰) equilibrated with quartz indicates a magmatic-hydrothermal source during stage I. A progressive addition of meteoric water component is suggested from stage I to IV of Zhengguang based on the average δ18Owater values equilibrated with quartz and homogenization temperatures (stage I: δ18Owater = 3.3‰, Th = 264 °C; stage II: δ18Owater = −1.4‰, Th = 182 °C; stage III: δ18Owater = −3.4‰, Th = 154 °C; stage IV: δ18Owater = −6.3‰, Th = 121 °C). Our new pyrite Re-Os dating result shows that Zhengguang formed at the same time with Tongshan and Duobaoshan within errors. Comparable sulfur isotopic compositions of pyrite from Zhengguang and Tongshan, analogous low-Fe content in sphalerite and similar mineral assemblage and alteration pattern between Zhengguang and East Tongshan IS veins collectively indicate a genetic connection between Zhengguang and Tongshan, which may derive from fluids exsolved from the same magma chamber. High-temperature assemblages (e.g., K-feldspr ± pyrite ± chalcopyrite) at Zhengguang indicate that there is potential for the discovery of porphyry copper–gold mineralization below the current level of diamond drilling. The confirmation of the Zhengguang as an Early Paleozoic Epithermal Deposit implies a good preservation and exploration potential of ancient Epithermal Deposits in eastern Central Asian Orogenic Belt.

  • gold behavior in intermediate sulfidation Epithermal systems a case study from the zhengguang gold Deposit heilongjiang province ne china
    Ore Geology Reviews, 2019
    Co-Authors: Guoxue Song, Kezhang Qin, Le Wang, Nigel J Cook, Cristiana L Ciobanu
    Abstract:

    Abstract The Zhengguang gold Deposit, a typical intermediate-sulfidation Epithermal Deposit, is located in the southeastern part of the Duobaoshan orefield, west of the Hegenshan-Heihe suture zone, in the eastern part of the Central Asian Orogenic Belt. The Deposit comprises five ore zones with total Au reserves exceeding 35 tonnes, with potential additional resources at depth. All vein-type orebodies are hosted by Paleozoic volcanic rocks and comprise multiple vein sets 1–100 cm in thickness. Although gold generally occurs in native form, or as electrum in Epithermal Deposits like Zhengguang, both pyrite and sphalerite are known to accommodate modest concentrations of invisible gold. This study employs a combination of petrography and sulfide chemistry to determine the role of invisible gold in the Zhengguang ores and the mechanisms of gold incorporation into Epithermal sulfides. Three sulfide stages are identified: an early quartz + pyrite (Py1a, Py1b) ± chalcopyrite (Ccp1) stage; a subsequent quartz + sphalerite (Sph2a, Sph2b) + pyrite (Py2a, Py2b, Py2c, Py2d) + chalcopyrite (Ccp2a, Ccp2b) ± galena ± calcite stage; and a late stage containing deformed quartz + pyrite (Py3a, Py3b) ± sphalerite. Petrography and sulfide chemistry allow three groups of pyrite (Au-poor, Au-rich, and a distinct Sb-rich group) to be distinguished, alongside three groups of chalcopyrite (Bi-rich, intermediate-Bi, and Bi-poor), and two groups of sphalerite (Au-poor, Au-rich). A potential porphyry system is indicated beneath the Epithermal system by the appearance of Au-poor pyrite and Bi-poor chalcopyrite. After precipitation of early Au-poor sulfides, inflow of relatively low temperature Epithermal fluids led to alteration and replacement of early porphyry-related sulfides, and to precipitation of Au-rich pyrite, Bi-rich and intermediate-Bi chalcopyrite, and sphalerite. Gold-rich pyrite contains up to 140 ppm Au, interpreted as both as lattice-scale substitution (Au1+) and as included particles of native gold (Au0). Epithermal chalcopyrite is an important silver carrier but, although Au is measurable, it is a not a good carrier for gold. A strong positive correlation between Au and Cu in pyrite from the first two stages indicate that gold and other metals were likely sourced from magma-derived hydrothermal fluids. The Deposit was formed in the Early Paleozoic but some gold ores appear deformed and partially destroyed by a later metamorphic event during which a distinct Sb-rich pyrite crystallized. This study should catalyze exploration in the orefield as it provides further support for an as-yet undiscovered porphyry system close to the Zhengguang Deposit.

  • volcanic subvolcanic rocks and tectonic setting of the zhengguang intermediate sulfidation Epithermal au zn Deposit eastern central asian orogenic belt ne china
    Journal of Asian Earth Sciences, 2018
    Co-Authors: Le Wang, Kezhang Qin, Guoxue Song, Xuyong Pang, Chao Zhao, Luying Jin, Xinyu Zou
    Abstract:

    Abstract The Zhengguang Au-Zn Deposit is a large Epithermal Deposit adjacent to the Tongshan and the Duobaoshan porphyry Cu Deposits in the Duobaoshan ore field, NE China. The host rocks mainly consist of andesite, andesitic tuff, and volcanic breccia. There are also many diorite dikes and subvolcanic rocks, including dacite porphyry and andesite porphyry. This contribution presents the zircon U-Pb ages, whole rock elemental and Sr-Nd isotopic compositions and zircon in situ Hf isotopic data for volcanic and subvolcanic rocks at Zhengguang. The dating results show that there are at least three episodes of magmatic events in the Zhengguang area: first, the extrusion of main host andesite of the Duobaoshan Formation (>490 Ma); second, the emplacement of copious andesitic dikes (490–470 Ma); and finally, early Silurian intermediate magmatic activity (440–436 Ma). The dacite porphyry emplaced at 480 Ma has relatively high SiO2 (63.5–64.7 wt%) and Sr (250–324 ppm) content, low Yb (0.59–0.67 ppm) and Y (5.65–6.63 ppm) content, and low initial 87Sr/86Sr ratios (0.7026–0.7031), suggesting an adakitic affinity. Given the positive eNd(t) values (+6.1 to + 7.1), eHf(t) values (+7.5 to + 13.5), high Mg# values (61–62), slightly high content of Cr (87.7–92.6 ppm), and Ni (37.6–46.9 ppm), we propose that the porphyry was derived from partial melting of subducted slabs of the Paleo-Asian oceanic plate with input from the mantle wedge during the ascent. The intermediate rocks can be divided into low Mg-andesitic rocks (LMAR, Mg# 33–54, Cr 14–144 ppm, and Ni 4–39 ppm) that originated from partial melting of the juvenile lower crust underplated by the mantle wedge-derived magma and high Mg-andesitic rocks (HMAR, Mg# 58–76, Cr 217–774 ppm, and Ni 81–419 ppm) derived from the partial melting of the slab fluid-metasomatic mantle wedge. The statistics of TDM2 of zircon Hf suggest that certain amounts of Neoproterozoic (particularly 800–600 Ma) continental crust growth were involved in the eastern part of the Central Asian Orogenic Belt (CAOB), as evidenced in the Zhengguang area. Based on the geological relationship and mineralization style, we suggest that the Zhengguang Deposit is an intermediate sulfidation Epithermal Deposit formed at ca. 480 Ma in a continental arc setting. Our work shows that Zhengguang is the oldest Epithermal Deposit in the CAOB and the oldest intermediate sulfidation (IS) Epithermal Deposit in the world. The identification of these characteristics is important for better understanding Epithermal Deposits in China and will add new insights about prospecting IS Deposits in similar tectonic settings, especially in the CAOB.

  • the nadun cu au mineralization central tibet root of a high sulfidation Epithermal Deposit
    Ore Geology Reviews, 2016
    Co-Authors: Kezhang Qin, Noreen J Evans, Junxing Zhao, Mingjian Cao, Fang Huang
    Abstract:

    Abstract A new high sulfidation Epithermal Cu–Au occurrence (Nadun) has been discovered adjacent to the Cretaceous Duolong porphyry Cu–Au Deposit within the Bangong–Nujiang metallogenic belt, central Tibet. The Nadun Cu–Au mineralization is hosted in a tectonic–hydrothermal breccia with advanced argillic alteration, which occurs above sandstone, associated with quartz–pyrite veins. The granodiorite porphyry with strong argillic alteration yields a zircon U–Pb age of 119.1 ± 1.3 Ma, whereas the weakly argillic granodiorite porphyry intruded into the breccia has a younger age of 116.1 ± 1.3 Ma. This indicates that Cu–Au Epithermal mineralization likely occurred between ~ 116 Ma and ~ 119 Ma, consistent with the duration of magmatic–hydrothermal activity at Duolong (~ 115–118 Ma), and providing evidence that Nadun and Duolong were formed during the same event. Moreover, the Nadun and Duolong porphyries have similar Hf isotopic compositions (eHf(t) values ranging from − 8.8 to 8.1; mean = 5.0 ± 1.1, n = 32), likely indicating that the Deposits are comagmatic. In addition, boiling assemblages in vapor-rich inclusions coexisting with brines occur in early stage quartz–pyrite veins, and likely record phase separation at a temperature of > 550–300 °C and pressure of 700–110 bars. Most liquid-rich fluid inclusions formed at the breccia stage show similar salinity (1.7–19.3 wt.% NaCl equiv) to vapor-rich inclusions from the underlying quartz–pyrite veins, likely indicating vapor contraction during cooling at elevated presssure. This suggests that quartz–pyrite veins may act as conduits for ore-forming fluid traveling from the porphyry to the Epithermal hydrothermal system. O and H isotopic compositions (δ18Ofluid = 0.42–9.71‰ and δD = − 102 to − 66‰) suggest that ore-forming fluids are dominantly from a magmatic source with a minor addition of meteoric water at a later stage. The S and Fe isotope compositions of sulfides (δ34S = − 5.9 to 0.5‰ and δ57Fe = − 2.15 to 0.17‰) decrease from the quartz–pyrite vein to breccia ore, indicating that ore-forming fluids gradually become SO42-enriched and relatively oxidized. This body of evidence suggests that the Nadun Cu–Au mineralization may represent the root of a high sulfidation Epithermal Deposit.

Le Wang - One of the best experts on this subject based on the ideXlab platform.

  • thermal history of an early paleozoic Epithermal Deposit constraints from 40ar 39ar and u th he thermochronology at zhengguang eastern central asian orogenic belt
    Ore Geology Reviews, 2020
    Co-Authors: Le Wang, Kezhang Qin, Noreen J Evans, Mingjian Cao, Martin Danisik, Guoxue Song, Xuyong Pang
    Abstract:

    Abstract The Zhengguang Epithermal Au-Zn Deposit, located in Heilongjiang Province, NE China, is an Early Paleozoic intermediate sulfidation Epithermal Deposit which is adjacent to the Duobaoshan and Tongshan porphyry Cu Deposits in the Duobaoshan magmatic arc, eastern Central Asian Orogenic Belt (CAOB). Our new 40Ar/39Ar dating presents plateau ages of 276.9 ± 1.2 Ma (MSWD = 1.5) for adularia and 265.7 ± 1.2 Ma (MSWD = 3.5) for illite. These ages are clearly younger than the mineralization age of Zhengguang (~480 Ma) and therefore represent a post-ore event which reset the adularia and illite argon systems. The resetting event could be related to post-collision of Xing’an Block and Songliao-Xilinhot Block. The weighted mean of zircon (U–Th)/He ages (ZHe) and apatite (U–Th)/He ages (AHe) from the same dacite porphyry with illite dating sample are 192 ± 10 Ma (MSWD = 2.2) and 98.8 ± 5.3 Ma (MSWD = 2.1), respectively. The ZHe age (~190 Ma) indicates a tectonothermal resetting event, possibly related to the development of Tongshan fault whereas the AHe age (~100 Ma) likely reflects 3 km-deep burial at Zhengguang. The intra-sample variations of (U–Th)/He ages for zircon grains are mainly due to radiation damage, while those for apatite are unknown. We argue that the post-ore volcanic eruption and slow uplift and exhumation rate caused by rollback of the Paleo-Pacific plate could facilitate burial and preservation of the Epithermal (and by inference porphyry) Deposits in NE China. Considering the complex collisional and amalgamation history in this area, we believe that there is exploration potential for ancient porphyry and Epithermal Deposits within the eastern section of the CAOB.

  • geology and genesis of the early paleozoic zhengguang intermediate sulfidation Epithermal au zn Deposit northeast china
    Ore Geology Reviews, 2020
    Co-Authors: Kezhang Qin, Le Wang, Guoxue Song, Xuyong Pang, Xinyu Zou
    Abstract:

    Abstract Zhengguang is a partly eroded (about ≥500 m being eroded), structurally controlled intermediate sulfidation (IS) Epithermal gold-zinc Deposit, characterized by wide distribution of base metal sulfides, Fe-poor sphalerite and Mn-calcite, hosted by the Late Cambrian-Early Ordovician basaltic-andesitic volcanic and volcano-sedimentary rocks in northeast China. The Deposit is located 4 and 8 km from the Early Ordovician Tongshan (including several IS veins about ~500 m away in the east called East Tongshan) and Duobaoshan porphyry copper Deposits, respectively. A 484.8 ± 8.7 Ma (MSWD = 198) of Re-Os isochron age on pyrite indicates that it is the most ancient intermediate sulfidation Deposit that has been dated. Four stages of veins have been discerned at Zhengguang. Early magnetite ± chalcopyrite ± epidote ± chlorite and K-feldspar ± pyrite ± chalcopyrite veins (stage I) were associated with restricted K-feldspar ± epidote (locally with chlorite) alteration and propylitic (epidote ± chlorite ± calcite) assemblages. Two primary Epithermal gold stages developed at Zhengguang: pyrite-quartz ± Fe-poor sphalerite ± chalcopyrite ± galena ± electrum ± petzite ± hessite ± tetrahedrite/tennantite ± adularia veins (stage II) and (Mn-)calcite-quartz-pyrite ± Fe-poor sphalerite ± chalcopyrite ± galena ± hessite ± native gold (stage III), plus a late barren stage characterized by little sulfides (calcite ± chlorite ± hematite ± quartz, stage IV). Gold occurs chiefly as micro-inclusions of electrum and petzite in pyrite and sphalerite of stages II and III. Stable isotope analyses and fluid inclusion results indicate a magmatic-hydrothermal component in the ore fluids. Fluid inclusion data from stage I yielded the highest salinity (∼6.9 wt% NaCl) and homogenization temperature (average 264 °C). Calculated oxygen isotope composition of fluid (δ18Owater up to 4.9‰) equilibrated with quartz indicates a magmatic-hydrothermal source during stage I. A progressive addition of meteoric water component is suggested from stage I to IV of Zhengguang based on the average δ18Owater values equilibrated with quartz and homogenization temperatures (stage I: δ18Owater = 3.3‰, Th = 264 °C; stage II: δ18Owater = −1.4‰, Th = 182 °C; stage III: δ18Owater = −3.4‰, Th = 154 °C; stage IV: δ18Owater = −6.3‰, Th = 121 °C). Our new pyrite Re-Os dating result shows that Zhengguang formed at the same time with Tongshan and Duobaoshan within errors. Comparable sulfur isotopic compositions of pyrite from Zhengguang and Tongshan, analogous low-Fe content in sphalerite and similar mineral assemblage and alteration pattern between Zhengguang and East Tongshan IS veins collectively indicate a genetic connection between Zhengguang and Tongshan, which may derive from fluids exsolved from the same magma chamber. High-temperature assemblages (e.g., K-feldspr ± pyrite ± chalcopyrite) at Zhengguang indicate that there is potential for the discovery of porphyry copper–gold mineralization below the current level of diamond drilling. The confirmation of the Zhengguang as an Early Paleozoic Epithermal Deposit implies a good preservation and exploration potential of ancient Epithermal Deposits in eastern Central Asian Orogenic Belt.

  • gold behavior in intermediate sulfidation Epithermal systems a case study from the zhengguang gold Deposit heilongjiang province ne china
    Ore Geology Reviews, 2019
    Co-Authors: Guoxue Song, Kezhang Qin, Le Wang, Nigel J Cook, Cristiana L Ciobanu
    Abstract:

    Abstract The Zhengguang gold Deposit, a typical intermediate-sulfidation Epithermal Deposit, is located in the southeastern part of the Duobaoshan orefield, west of the Hegenshan-Heihe suture zone, in the eastern part of the Central Asian Orogenic Belt. The Deposit comprises five ore zones with total Au reserves exceeding 35 tonnes, with potential additional resources at depth. All vein-type orebodies are hosted by Paleozoic volcanic rocks and comprise multiple vein sets 1–100 cm in thickness. Although gold generally occurs in native form, or as electrum in Epithermal Deposits like Zhengguang, both pyrite and sphalerite are known to accommodate modest concentrations of invisible gold. This study employs a combination of petrography and sulfide chemistry to determine the role of invisible gold in the Zhengguang ores and the mechanisms of gold incorporation into Epithermal sulfides. Three sulfide stages are identified: an early quartz + pyrite (Py1a, Py1b) ± chalcopyrite (Ccp1) stage; a subsequent quartz + sphalerite (Sph2a, Sph2b) + pyrite (Py2a, Py2b, Py2c, Py2d) + chalcopyrite (Ccp2a, Ccp2b) ± galena ± calcite stage; and a late stage containing deformed quartz + pyrite (Py3a, Py3b) ± sphalerite. Petrography and sulfide chemistry allow three groups of pyrite (Au-poor, Au-rich, and a distinct Sb-rich group) to be distinguished, alongside three groups of chalcopyrite (Bi-rich, intermediate-Bi, and Bi-poor), and two groups of sphalerite (Au-poor, Au-rich). A potential porphyry system is indicated beneath the Epithermal system by the appearance of Au-poor pyrite and Bi-poor chalcopyrite. After precipitation of early Au-poor sulfides, inflow of relatively low temperature Epithermal fluids led to alteration and replacement of early porphyry-related sulfides, and to precipitation of Au-rich pyrite, Bi-rich and intermediate-Bi chalcopyrite, and sphalerite. Gold-rich pyrite contains up to 140 ppm Au, interpreted as both as lattice-scale substitution (Au1+) and as included particles of native gold (Au0). Epithermal chalcopyrite is an important silver carrier but, although Au is measurable, it is a not a good carrier for gold. A strong positive correlation between Au and Cu in pyrite from the first two stages indicate that gold and other metals were likely sourced from magma-derived hydrothermal fluids. The Deposit was formed in the Early Paleozoic but some gold ores appear deformed and partially destroyed by a later metamorphic event during which a distinct Sb-rich pyrite crystallized. This study should catalyze exploration in the orefield as it provides further support for an as-yet undiscovered porphyry system close to the Zhengguang Deposit.

  • volcanic subvolcanic rocks and tectonic setting of the zhengguang intermediate sulfidation Epithermal au zn Deposit eastern central asian orogenic belt ne china
    Journal of Asian Earth Sciences, 2018
    Co-Authors: Le Wang, Kezhang Qin, Guoxue Song, Xuyong Pang, Chao Zhao, Luying Jin, Xinyu Zou
    Abstract:

    Abstract The Zhengguang Au-Zn Deposit is a large Epithermal Deposit adjacent to the Tongshan and the Duobaoshan porphyry Cu Deposits in the Duobaoshan ore field, NE China. The host rocks mainly consist of andesite, andesitic tuff, and volcanic breccia. There are also many diorite dikes and subvolcanic rocks, including dacite porphyry and andesite porphyry. This contribution presents the zircon U-Pb ages, whole rock elemental and Sr-Nd isotopic compositions and zircon in situ Hf isotopic data for volcanic and subvolcanic rocks at Zhengguang. The dating results show that there are at least three episodes of magmatic events in the Zhengguang area: first, the extrusion of main host andesite of the Duobaoshan Formation (>490 Ma); second, the emplacement of copious andesitic dikes (490–470 Ma); and finally, early Silurian intermediate magmatic activity (440–436 Ma). The dacite porphyry emplaced at 480 Ma has relatively high SiO2 (63.5–64.7 wt%) and Sr (250–324 ppm) content, low Yb (0.59–0.67 ppm) and Y (5.65–6.63 ppm) content, and low initial 87Sr/86Sr ratios (0.7026–0.7031), suggesting an adakitic affinity. Given the positive eNd(t) values (+6.1 to + 7.1), eHf(t) values (+7.5 to + 13.5), high Mg# values (61–62), slightly high content of Cr (87.7–92.6 ppm), and Ni (37.6–46.9 ppm), we propose that the porphyry was derived from partial melting of subducted slabs of the Paleo-Asian oceanic plate with input from the mantle wedge during the ascent. The intermediate rocks can be divided into low Mg-andesitic rocks (LMAR, Mg# 33–54, Cr 14–144 ppm, and Ni 4–39 ppm) that originated from partial melting of the juvenile lower crust underplated by the mantle wedge-derived magma and high Mg-andesitic rocks (HMAR, Mg# 58–76, Cr 217–774 ppm, and Ni 81–419 ppm) derived from the partial melting of the slab fluid-metasomatic mantle wedge. The statistics of TDM2 of zircon Hf suggest that certain amounts of Neoproterozoic (particularly 800–600 Ma) continental crust growth were involved in the eastern part of the Central Asian Orogenic Belt (CAOB), as evidenced in the Zhengguang area. Based on the geological relationship and mineralization style, we suggest that the Zhengguang Deposit is an intermediate sulfidation Epithermal Deposit formed at ca. 480 Ma in a continental arc setting. Our work shows that Zhengguang is the oldest Epithermal Deposit in the CAOB and the oldest intermediate sulfidation (IS) Epithermal Deposit in the world. The identification of these characteristics is important for better understanding Epithermal Deposits in China and will add new insights about prospecting IS Deposits in similar tectonic settings, especially in the CAOB.

Zhaoshan Chang - One of the best experts on this subject based on the ideXlab platform.

  • the paleozoic mount carlton Deposit bowen basin northeast australia shallow high sulfidation Epithermal au ag cu mineralization formed during rifting
    Economic Geology, 2018
    Co-Authors: Fredrik Sahlström, Isaac Corral, Paul H G M Dirks, Antonio Arribas, Matthew Obiriyeboah, Zhaoshan Chang, Chris Hall
    Abstract:

    Mount Carlton is a Paleozoic high-sulfidation Epithermal Deposit located in the northern segment of the Bowen Basin, northeast Queensland, Australia. The Deposit is hosted in Early Permian volcanic and sedimentary rocks, and an open-pit mining operation includes the Au-rich V2 pit in the northeast and the Ag-rich A39 pit in the southwest. Mineralization at Mt. Carlton occurred during active rifting, partly contemporaneously with the Deposition of volcanic sediments in localized half-graben and graben basins. Steep normal faults and fracture networks related to the rifting acted as fluid conduits and localized cores of silicic alteration. The silicic cores transition outward to zones of quartz-alunite alteration, which are, in turn, enveloped by a zone of quartz-dickite-kaolinite alteration. Epithermal mineralization at Mt. Carlton developed in three stages: Cu-Au-Ag mineralization dominated by enargite was overprinted by Zn-Pb-Au-Ag mineralization dominated by sphalerite, which, in turn, was overprinted by Cu-Au-Ag mineralization dominated by tennantite. Proximal Au-Cu mineralization in the V2 pit occurs in networks of steep faults associated with veins and hydrothermal breccias within a massive rhyodacite porphyry. Three distinct ore zones (Eastern, Western, and Link) are aligned, en echelon, along a broadly E trending corridor. The Western ore zone continues along ~600-m strike length to the southwest into the A39 pit, and it shows a metal zonation, from proximal to distal, of Au-Cu → Cu-Zn-Pb-Ag → Ag-Pb-(Cu) → Ag. Distal Ag mineralization in the A39 pit is concentrated in a volcanolacustrine sedimentary sequence that overlies the rhyodacite porphyry. It occurs in a stratabound position oriented parallel to primary sedimentary layering and locally exhibits synsedimentary ore textures. Such textures are interpreted to have formed as mineralizing fluids discharged into what most likely were lakes developed within localized rift basins, at the same time that the volcanolacustrine sediments were Deposited. At depth, equivalent ore textures were produced within open spaces in the structural roots of the rift basins. 40Ar/39Ar dating of hydrothermal alunite yielded an age range of 284 ± 7 to 277 ± 7 Ma, which links the formation of the Mt. Carlton Deposit to the Early Permian back-arc rifting stage in the Bowen Basin. Prolonged extension provided rapid burial of the Deposit beneath a postmineralization, volcanosedimentary cover, which was essential for the exceptional preservation of Mt. Carlton. The same extension caused displacement of the rock pile along a series of shallowly dipping detachment faults and segmentation and rotation of the ore zones across steeply dipping normal faults. This deformation would have displaced any underlying porphyry mineralization relative to the current location of Mt. Carlton.

  • hyperspectral cathodoluminescence study of indium bearing sphalerite from the mt carlton high sulphidation Epithermal Deposit queensland australia
    European Journal of Mineralogy, 2017
    Co-Authors: Fredrik Sahlström, Isaac Corral, Kevin Blake, Zhaoshan Chang
    Abstract:

    Sphalerite is the most important host mineral for the recovery of indium. New techniques to study the presence and distribution of this critical metal in sphalerite can therefore be of interest for scientific and technological purposes alike. In this study we use the emerging tool of hyperspectral cathodoluminescence (CL) mapping, combined with X-ray element mapping and spot analyses, to characterise the composition and CL properties of indium-bearing sphalerite from the Mt Carlton high-sulphidation Epithermal Deposit (NE Queensland, Australia). Mt Carlton sphalerite contains highly elevated concentrations of indium (up to 19.59 wt%) occurring within similar to 1 mu m thick colloform bands, which show an average composition of (Zn0.63Cu0.20In0.15Ga0.01) S-0.96. Indium, Cu and Ga are interpreted to have been incorporated via the coupled substitution 2Zn(2+) Cu+(In, Ga) (3+). Hyperspectral CL mapping reveals a high-intensity CL emission directly related to In-Cu-(Ga)-rich sphalerite, centred at wavelengths between similar to 500 and similar to 600 nm. The CL peak is shifted to the higher-wavelength positions when the proportion of In relative to Cu increases. Our study shows that hyperspectral CL mapping is a powerful and efficient technique to study the distribution of In in sphalerite.

  • Mineralogical Distribution of Germanium, Gallium and Indium at the Mt Carlton High-Sulfidation Epithermal Deposit, NE Australia, and Comparison with Similar Deposits Worldwide
    MDPI AG, 2017
    Co-Authors: Fredrik Sahlström, Isaac Corral, Antonio Arribas, Paul Dirks, Zhaoshan Chang
    Abstract:

    Germanium, gallium and indium are in high demand due to their growing usage in high-tech and green-tech applications. However, the mineralogy and the mechanisms of concentration of these critical elements in different types of hydrothermal ore Deposits remain poorly constrained. We investigated the mineralogical distribution of Ge, Ga and In at the Mt Carlton high-sulfidation Epithermal Deposit in NE Australia, using electron probe microanalysis and laser ablation inductively-coupled plasma mass spectrometry. Parageneses from which selected minerals were analyzed include: Stage 1 acid sulfate alteration (alunite), Stage 2A high-sulfidation enargite mineralization (enargite, argyrodite, sphalerite, pyrite, barite), Stage 2B intermediate-sulfidation sphalerite mineralization (sphalerite, pyrite, galena) and Stage 3 hydrothermal void fill (dickite). Moderate to locally high concentrations of Ga were measured in Stage 1 alunite (up to 339 ppm) and in Stage 3 dickite (up to 150 ppm). The Stage 2A ores show enrichment in Ge, which is primarily associated with argyrodite (up to 6.95 wt % Ge) and Ge-bearing enargite (up to 2189 ppm Ge). Co-existing sphalerite has comparatively low Ge content (up to 143 ppm), while Ga (up to 1181 ppm) and In (up to 571 ppm) are higher. Sphalerite in Stage 2B contains up to 611 ppm Ge, 2829 ppm Ga and 2169 ppm In, and locally exhibits fine colloform bands of an uncharacterized Zn-In mineral with compositions close to CuZn2(In,Ga)S4. Barite, pyrite and galena which occur in association with Stage 2 mineralization were found to play negligible roles as carriers of Ge, Ga and In at Mt Carlton. Analyzed reference samples of enargite from seven similar Deposits worldwide have average Ge concentrations ranging from 12 to 717 ppm (maximum 2679 ppm). The Deposits from which samples showed high enrichment in critical elements in this study are all hosted in stratigraphic sequences that locally contain carbonaceous sedimentary rocks. In addition to magmatic-hydrothermal processes, such rocks could potentially be important for the concentration of critical elements in high-sulfidation Epithermal Deposits

  • hydrothermal alteration and mineralisation at the mt carlton high sulphidation au ag cu Epithermal Deposit ne queensland australia
    2016
    Co-Authors: Fredrik Sahlström, Corral I Calleja, M Stokes, M Pocock, D. Hewitt, Paul H G M Dirks, Antonio Arribas, Zhaoshan Chang, Matthew Obiriyeboah
    Abstract:

    The Mt Carlton high-sulphidation Au-Ag-Cu Deposit is located in the northern Bowen Basin, NE Queensland (Australia). High-grade mineralisation is confined to NE-trending, steeply dipping (75-90°) structures, and is hosted in a rhyodacitic unit of the Lizzie Creek Volcanic Group (Early Permian). The core of the hydrothermal system shows silicic alteration, with variable amounts of alunite (disseminated-and vein-type), anhydrite and pyrite. Outwards, the silicic zone progressively grades into an envelope of quartz- alunite-barite-pyrite → quartz-dickite-kaolinite-pyrite → illite-montmorillonite-pyrite alteration. After the alteration, the majority of metals were Deposited in an initial stage of high-sulphidation mineralisation, dominated by enargite-luzonite-pyrite. This stage is overprinted by two intermediate-sulphidation stages, one Zn-Pb-Au rich (sphalerite-galena-electrum) and one Cu-(Au) rich (tennantite), respectively. The known mineralisation along ~800m strike length shows a distinct metal zonation from NE to SW of Cu-Au→ Cu+Zn+Pb+Ag →Ag+Pb →Ag. This metal zonation is mainly linked to the mineralogy of the initial high- sulphidation ore stage. Ar-Ar dating of alunite from the Mt Carlton lithocap gives an age of 284.3 ± 2.0 Ma. It is not distinguishable from U-Pb ages of the Lizzie Creek volcanic rocks (283-287 ± 2-4 Ma), indicating that the mineralisation occurred shortly after the formation of the host rocks. Stable isotope analyses (S, O, H) of sulfates (alunite, anhydrite and barite) and coeval pyrite suggest that they formed from a SO42- -dominated fluid with a mixed magmatic-meteoric signature. Thermometric calculations based on S isotope pairs indicate a temperature range of ~220-130 °C for the hydrothermal alteration stage (alunite-pyrite), and ~130-115 °C for late, intermediate-sulphidation ore (sphalerite-galena, sphalerite-pyrite). The combined petrographic and isotopic evidence thus suggest that a cooling fluid that evolved from high - to intermediate-sulphidation states was involved in the genesis of the Mt Carlton Deposit.

  • constraints on the ore fluids in the chah zard breccia hosted Epithermal au ag Deposit iran fluid inclusions and stable isotope studies
    Ore Geology Reviews, 2015
    Co-Authors: Hossein Kouhestani, Zhaoshan Chang, Majid Ghaderi, Khin Zaw
    Abstract:

    The Chah Zard gold–silver Deposit, in the central part of the Urumieh-Dokhtar Magmatic Arc (UDMA) of Iran, is a breccia-hosted low- to intermediate-sulfidation Epithermal Deposit with a resource of ~ 2.5 Mt averaging 1.7 g/t Au and 12.7 g/t Ag. Gold and silver mineralization occurs in breccia and veins associated with a 6.2 ± 0.2 Ma volcanic complex. Microthermometric measurements on quartz- and sphalerite-hosted, two-phase liquid-rich fluid inclusions indicate that the mineralization may have taken place between 260 and 345 °C, from a moderately saline hydrothermal fluid (8.4–13.7 wt.% NaCl equiv.). First ice-melting temperatures between − 37 and − 53 °C indicate that the aqueous fluids contained NaCl, CaCl2 ± MgCl2 ± FeCl2. Coexisting liquid-rich and vapor-rich fluid inclusions in quartz and sphalerite provide evidence for boiling in ore-stage breccia and veins. Additionally, the occurrence of adularia and bladed calcite in high-grade ore zones and the presence of hydrothermal breccias and chalcedonic quartz are consistent with boiling. Calculated δ18O values of water in equilibrium with quartz (+ 3.4 to + 13.1‰) suggest that the fluid may have had a magmatic source, but was 18O-depleted by mixing with meteoric water. The average calculated δ34SH2S values are − 0.2‰ for pyrite, + 0.2‰ for chalcopyrite, − 1.0‰ for sphalerite and − 0.2‰ for galena. The δ34SH2S values are consistent with a magmatic source for sulfur. Gold Deposition at Chah Zard is inferred to have been largely caused by boiling, although fluid mixing and/or wall rock reactions may also have occurred. After rising to a depth of between 970 and 440 m, the fluid boiled, causing Deposition of fine-grained quartz, and sealing of the hydrothermal conduit. Episodic boiling in response to alternating silica sealing and hydraulic brecciation was responsible for ore Deposition. Gold and silver may have precipitated due to the destabilization of HS− complexes, caused by the boiling-off of H2S to vapor, whereas the dilution and/or cooling of hydrothermal fluids led to the precipitation of base metals.

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  • thermal history of an early paleozoic Epithermal Deposit constraints from 40ar 39ar and u th he thermochronology at zhengguang eastern central asian orogenic belt
    Ore Geology Reviews, 2020
    Co-Authors: Le Wang, Kezhang Qin, Noreen J Evans, Mingjian Cao, Martin Danisik, Guoxue Song, Xuyong Pang
    Abstract:

    Abstract The Zhengguang Epithermal Au-Zn Deposit, located in Heilongjiang Province, NE China, is an Early Paleozoic intermediate sulfidation Epithermal Deposit which is adjacent to the Duobaoshan and Tongshan porphyry Cu Deposits in the Duobaoshan magmatic arc, eastern Central Asian Orogenic Belt (CAOB). Our new 40Ar/39Ar dating presents plateau ages of 276.9 ± 1.2 Ma (MSWD = 1.5) for adularia and 265.7 ± 1.2 Ma (MSWD = 3.5) for illite. These ages are clearly younger than the mineralization age of Zhengguang (~480 Ma) and therefore represent a post-ore event which reset the adularia and illite argon systems. The resetting event could be related to post-collision of Xing’an Block and Songliao-Xilinhot Block. The weighted mean of zircon (U–Th)/He ages (ZHe) and apatite (U–Th)/He ages (AHe) from the same dacite porphyry with illite dating sample are 192 ± 10 Ma (MSWD = 2.2) and 98.8 ± 5.3 Ma (MSWD = 2.1), respectively. The ZHe age (~190 Ma) indicates a tectonothermal resetting event, possibly related to the development of Tongshan fault whereas the AHe age (~100 Ma) likely reflects 3 km-deep burial at Zhengguang. The intra-sample variations of (U–Th)/He ages for zircon grains are mainly due to radiation damage, while those for apatite are unknown. We argue that the post-ore volcanic eruption and slow uplift and exhumation rate caused by rollback of the Paleo-Pacific plate could facilitate burial and preservation of the Epithermal (and by inference porphyry) Deposits in NE China. Considering the complex collisional and amalgamation history in this area, we believe that there is exploration potential for ancient porphyry and Epithermal Deposits within the eastern section of the CAOB.

  • geology and genesis of the early paleozoic zhengguang intermediate sulfidation Epithermal au zn Deposit northeast china
    Ore Geology Reviews, 2020
    Co-Authors: Kezhang Qin, Le Wang, Guoxue Song, Xuyong Pang, Xinyu Zou
    Abstract:

    Abstract Zhengguang is a partly eroded (about ≥500 m being eroded), structurally controlled intermediate sulfidation (IS) Epithermal gold-zinc Deposit, characterized by wide distribution of base metal sulfides, Fe-poor sphalerite and Mn-calcite, hosted by the Late Cambrian-Early Ordovician basaltic-andesitic volcanic and volcano-sedimentary rocks in northeast China. The Deposit is located 4 and 8 km from the Early Ordovician Tongshan (including several IS veins about ~500 m away in the east called East Tongshan) and Duobaoshan porphyry copper Deposits, respectively. A 484.8 ± 8.7 Ma (MSWD = 198) of Re-Os isochron age on pyrite indicates that it is the most ancient intermediate sulfidation Deposit that has been dated. Four stages of veins have been discerned at Zhengguang. Early magnetite ± chalcopyrite ± epidote ± chlorite and K-feldspar ± pyrite ± chalcopyrite veins (stage I) were associated with restricted K-feldspar ± epidote (locally with chlorite) alteration and propylitic (epidote ± chlorite ± calcite) assemblages. Two primary Epithermal gold stages developed at Zhengguang: pyrite-quartz ± Fe-poor sphalerite ± chalcopyrite ± galena ± electrum ± petzite ± hessite ± tetrahedrite/tennantite ± adularia veins (stage II) and (Mn-)calcite-quartz-pyrite ± Fe-poor sphalerite ± chalcopyrite ± galena ± hessite ± native gold (stage III), plus a late barren stage characterized by little sulfides (calcite ± chlorite ± hematite ± quartz, stage IV). Gold occurs chiefly as micro-inclusions of electrum and petzite in pyrite and sphalerite of stages II and III. Stable isotope analyses and fluid inclusion results indicate a magmatic-hydrothermal component in the ore fluids. Fluid inclusion data from stage I yielded the highest salinity (∼6.9 wt% NaCl) and homogenization temperature (average 264 °C). Calculated oxygen isotope composition of fluid (δ18Owater up to 4.9‰) equilibrated with quartz indicates a magmatic-hydrothermal source during stage I. A progressive addition of meteoric water component is suggested from stage I to IV of Zhengguang based on the average δ18Owater values equilibrated with quartz and homogenization temperatures (stage I: δ18Owater = 3.3‰, Th = 264 °C; stage II: δ18Owater = −1.4‰, Th = 182 °C; stage III: δ18Owater = −3.4‰, Th = 154 °C; stage IV: δ18Owater = −6.3‰, Th = 121 °C). Our new pyrite Re-Os dating result shows that Zhengguang formed at the same time with Tongshan and Duobaoshan within errors. Comparable sulfur isotopic compositions of pyrite from Zhengguang and Tongshan, analogous low-Fe content in sphalerite and similar mineral assemblage and alteration pattern between Zhengguang and East Tongshan IS veins collectively indicate a genetic connection between Zhengguang and Tongshan, which may derive from fluids exsolved from the same magma chamber. High-temperature assemblages (e.g., K-feldspr ± pyrite ± chalcopyrite) at Zhengguang indicate that there is potential for the discovery of porphyry copper–gold mineralization below the current level of diamond drilling. The confirmation of the Zhengguang as an Early Paleozoic Epithermal Deposit implies a good preservation and exploration potential of ancient Epithermal Deposits in eastern Central Asian Orogenic Belt.

  • gold behavior in intermediate sulfidation Epithermal systems a case study from the zhengguang gold Deposit heilongjiang province ne china
    Ore Geology Reviews, 2019
    Co-Authors: Guoxue Song, Kezhang Qin, Le Wang, Nigel J Cook, Cristiana L Ciobanu
    Abstract:

    Abstract The Zhengguang gold Deposit, a typical intermediate-sulfidation Epithermal Deposit, is located in the southeastern part of the Duobaoshan orefield, west of the Hegenshan-Heihe suture zone, in the eastern part of the Central Asian Orogenic Belt. The Deposit comprises five ore zones with total Au reserves exceeding 35 tonnes, with potential additional resources at depth. All vein-type orebodies are hosted by Paleozoic volcanic rocks and comprise multiple vein sets 1–100 cm in thickness. Although gold generally occurs in native form, or as electrum in Epithermal Deposits like Zhengguang, both pyrite and sphalerite are known to accommodate modest concentrations of invisible gold. This study employs a combination of petrography and sulfide chemistry to determine the role of invisible gold in the Zhengguang ores and the mechanisms of gold incorporation into Epithermal sulfides. Three sulfide stages are identified: an early quartz + pyrite (Py1a, Py1b) ± chalcopyrite (Ccp1) stage; a subsequent quartz + sphalerite (Sph2a, Sph2b) + pyrite (Py2a, Py2b, Py2c, Py2d) + chalcopyrite (Ccp2a, Ccp2b) ± galena ± calcite stage; and a late stage containing deformed quartz + pyrite (Py3a, Py3b) ± sphalerite. Petrography and sulfide chemistry allow three groups of pyrite (Au-poor, Au-rich, and a distinct Sb-rich group) to be distinguished, alongside three groups of chalcopyrite (Bi-rich, intermediate-Bi, and Bi-poor), and two groups of sphalerite (Au-poor, Au-rich). A potential porphyry system is indicated beneath the Epithermal system by the appearance of Au-poor pyrite and Bi-poor chalcopyrite. After precipitation of early Au-poor sulfides, inflow of relatively low temperature Epithermal fluids led to alteration and replacement of early porphyry-related sulfides, and to precipitation of Au-rich pyrite, Bi-rich and intermediate-Bi chalcopyrite, and sphalerite. Gold-rich pyrite contains up to 140 ppm Au, interpreted as both as lattice-scale substitution (Au1+) and as included particles of native gold (Au0). Epithermal chalcopyrite is an important silver carrier but, although Au is measurable, it is a not a good carrier for gold. A strong positive correlation between Au and Cu in pyrite from the first two stages indicate that gold and other metals were likely sourced from magma-derived hydrothermal fluids. The Deposit was formed in the Early Paleozoic but some gold ores appear deformed and partially destroyed by a later metamorphic event during which a distinct Sb-rich pyrite crystallized. This study should catalyze exploration in the orefield as it provides further support for an as-yet undiscovered porphyry system close to the Zhengguang Deposit.

  • volcanic subvolcanic rocks and tectonic setting of the zhengguang intermediate sulfidation Epithermal au zn Deposit eastern central asian orogenic belt ne china
    Journal of Asian Earth Sciences, 2018
    Co-Authors: Le Wang, Kezhang Qin, Guoxue Song, Xuyong Pang, Chao Zhao, Luying Jin, Xinyu Zou
    Abstract:

    Abstract The Zhengguang Au-Zn Deposit is a large Epithermal Deposit adjacent to the Tongshan and the Duobaoshan porphyry Cu Deposits in the Duobaoshan ore field, NE China. The host rocks mainly consist of andesite, andesitic tuff, and volcanic breccia. There are also many diorite dikes and subvolcanic rocks, including dacite porphyry and andesite porphyry. This contribution presents the zircon U-Pb ages, whole rock elemental and Sr-Nd isotopic compositions and zircon in situ Hf isotopic data for volcanic and subvolcanic rocks at Zhengguang. The dating results show that there are at least three episodes of magmatic events in the Zhengguang area: first, the extrusion of main host andesite of the Duobaoshan Formation (>490 Ma); second, the emplacement of copious andesitic dikes (490–470 Ma); and finally, early Silurian intermediate magmatic activity (440–436 Ma). The dacite porphyry emplaced at 480 Ma has relatively high SiO2 (63.5–64.7 wt%) and Sr (250–324 ppm) content, low Yb (0.59–0.67 ppm) and Y (5.65–6.63 ppm) content, and low initial 87Sr/86Sr ratios (0.7026–0.7031), suggesting an adakitic affinity. Given the positive eNd(t) values (+6.1 to + 7.1), eHf(t) values (+7.5 to + 13.5), high Mg# values (61–62), slightly high content of Cr (87.7–92.6 ppm), and Ni (37.6–46.9 ppm), we propose that the porphyry was derived from partial melting of subducted slabs of the Paleo-Asian oceanic plate with input from the mantle wedge during the ascent. The intermediate rocks can be divided into low Mg-andesitic rocks (LMAR, Mg# 33–54, Cr 14–144 ppm, and Ni 4–39 ppm) that originated from partial melting of the juvenile lower crust underplated by the mantle wedge-derived magma and high Mg-andesitic rocks (HMAR, Mg# 58–76, Cr 217–774 ppm, and Ni 81–419 ppm) derived from the partial melting of the slab fluid-metasomatic mantle wedge. The statistics of TDM2 of zircon Hf suggest that certain amounts of Neoproterozoic (particularly 800–600 Ma) continental crust growth were involved in the eastern part of the Central Asian Orogenic Belt (CAOB), as evidenced in the Zhengguang area. Based on the geological relationship and mineralization style, we suggest that the Zhengguang Deposit is an intermediate sulfidation Epithermal Deposit formed at ca. 480 Ma in a continental arc setting. Our work shows that Zhengguang is the oldest Epithermal Deposit in the CAOB and the oldest intermediate sulfidation (IS) Epithermal Deposit in the world. The identification of these characteristics is important for better understanding Epithermal Deposits in China and will add new insights about prospecting IS Deposits in similar tectonic settings, especially in the CAOB.

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  • a model of boiling for fluid inclusion studies application to the bolanos ag au pb zn Epithermal Deposit western mexico
    Journal of Geochemical Exploration, 2011
    Co-Authors: Carles Canet, Sara I Franco, Rosa Maria Prolledesma, Eduardo Gonzalezpartida, Ruth Esther Villanuevaestrada
    Abstract:

    article i nfo Boiling can be inferred from fluid inclusion microthermometry studies when a progressive increase in apparent salinity is observed along with a decrease of homogenization temperature (TH) and depth, thus reflecting the partitioning of non-volatile solutes into the liquid phase during steam loss. We propose a model for fluid evolution during boiling based on mass and heat balance equations, which establishes paths in the TH-salinity space that can be compared with fluid inclusion data to confirm or discard boiling. Additionally, the model allows calculating paleo-depths, for which the effect of steam bubbles lowering the hydrostatic pressure is taken into account. The Bolanos Ag-Au-Pb-Zn Deposit was selected to test the suitability of the proposed model, given that previous work in this Deposit emphasizes the role of boiling in ore Deposition. The Bolanos Deposit belongs to the low-sulfidation Epithermal type and is genetically related to the final stage of formation of a graben-type caldera. Microthermometry data show that the deeper the sample was taken, the higher is TH and the lower is salinity (sample depths: 540, 500, 440 and 200 m below present surface). The overall range (n=108) of variation of TH and salinity is of 137°-279 °C and 2.4-10.9 wt.% NaCl eq., respectively. According to our model, rising hydrothermal fluids in Bolanos underwent boiling from depths not exceeding 440 m (below present surface). Conversely, below this level fluid evolution cannot be explained in terms of boiling, because the increase of salinity is much greater than the expected considering solely the amount of steam lost during the corresponding drop of temperature. The calculated paleo-depth for the lowest level of boiling in a Bolanos vein is ~435 m. Neglecting the drop in fluid density due to steam bubbles may lead to serious underestimations of paleo-depths.

  • a model of boiling for fluid inclusion studies application to the bolanos ag au pb zn Epithermal Deposit western mexico
    Journal of Geochemical Exploration, 2011
    Co-Authors: Carles Canet, Sara I Franco, Rosa Maria Prolledesma, Eduardo Gonzalezpartida, Ruth Esther Villanuevaestrada
    Abstract:

    Abstract Boiling can be inferred from fluid inclusion microthermometry studies when a progressive increase in apparent salinity is observed along with a decrease of homogenization temperature (TH) and depth, thus reflecting the partitioning of non-volatile solutes into the liquid phase during steam loss. We propose a model for fluid evolution during boiling based on mass and heat balance equations, which establishes paths in the TH-salinity space that can be compared with fluid inclusion data to confirm or discard boiling. Additionally, the model allows calculating paleo-depths, for which the effect of steam bubbles lowering the hydrostatic pressure is taken into account. The Bolanos Ag–Au–Pb–Zn Deposit was selected to test the suitability of the proposed model, given that previous work in this Deposit emphasizes the role of boiling in ore Deposition. The Bolanos Deposit belongs to the low-sulfidation Epithermal type and is genetically related to the final stage of formation of a graben-type caldera. Microthermometry data show that the deeper the sample was taken, the higher is TH and the lower is salinity (sample depths: 540, 500, 440 and 200 m below present surface). The overall range (n = 108) of variation of TH and salinity is of 137°–279 °C and 2.4–10.9 wt.% NaCl eq., respectively. According to our model, rising hydrothermal fluids in Bolanos underwent boiling from depths not exceeding 440 m (below present surface). Conversely, below this level fluid evolution cannot be explained in terms of boiling, because the increase of salinity is much greater than the expected considering solely the amount of steam lost during the corresponding drop of temperature. The calculated paleo-depth for the lowest level of boiling in a Bolanos vein is ~ 435 m. Neglecting the drop in fluid density due to steam bubbles may lead to serious underestimations of paleo-depths.

  • fluid sources for the la guitarra Epithermal Deposit temascaltepec district mexico volatile and helium isotope analyses in fluid inclusions
    Chemical Geology, 2006
    Co-Authors: Antoni Camprubi, Ruth Esther Villanuevaestrada, Beverly Chomiak, Angels Canals, David I Norman, Esteve Cardellach, Martin Stute
    Abstract:

    The La Guitarra Deposit (Temascaltepec district, South-Central Mexico), belongs to the low/intermediate sulfidation Epithermal type, has a polymetallic character although it is currently being mined for Ag and Au. The mineralization shows a polyphasic character and formed through several stages and sub-stages (named I, IIA, IIB, IIC, IID, and III). The previous structural, mineralogical, fluid inclusion and stable isotope studies were used to constrain the selection of samples for volatile and helium isotope analyses portrayed in this study. The N2/Ar overall range obtained from analytical runs on fluid inclusion volatiles, by means of Quadrupole Mass Spectrometry (QMS), is 0 to 2526, and it ranges 0 to 2526 for stage I, 0 to 1264 for stage IIA, 0 to 1369 for stage IIB, 11 to 2401 for stage IIC, 19 to 324 for stage IID, and 0 to 2526 for stage III. These values, combined with the CO2/ CH4 ratios, and N2–He–Ar and N2–CH4–Ar relationships, suggest the occurrence of fluids from magmatic, crustal, and shallow meteoric sources in the forming Epithermal vein Deposit. The helium isotope analyses, obtained by means of Noble Gas Mass Spectrometry, display R/Ra average values between 0.5 and 2, pointing to the occurrence of mantle-derived helium that was relatively diluted or “contaminated” by crustal helium. These volatile analyses, when correlated with the stable isotope data from previous works and He isotope data, show the same distribution of data concerning sources for mineralizing fluids, especially those corresponding to magmatic and crustal sources. Thus, the overall geochemical data from mineralizing fluids are revealed as intrinsically consistent when compared to each other. The three main sources for mineralizing fluids (magmatic, and both deep and shallow meteoric fluids) are accountable at any scale, from stages of mineralization down to specific mineral associations. The volatile and helium isotope data obtained in this paper suggest that the precious metal-bearing mineral associations formed after hydrothermal pulses of predominantly oxidized