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Léon Dejonghe - One of the best experts on this subject based on the ideXlab platform.

  • zinc lead Deposits of belgium
    Ore Geology Reviews, 1998
    Co-Authors: Léon Dejonghe
    Abstract:

    The exploitation of Belgian zinc–lead Deposits dates back to prehistoric times. Its apogee was between 1850 and 1870 and the last mine was closed in 1946. During the period 1837–1945, during which time production levels were recorded, the tonnage of exploited metals reached about 1 500 000 tons Pb+Zn with a Zn/Pb ratio of 8–9. The mineralogy of the Deposits is generally simple: sphalerite, galena, pyrite or marcasite, and locally Ni- and Co-sulfides. Several ore Deposit types may be distinguished, including syndiagenetic-, vein and connected flat-, and paleokarstic types. The syndiagenetic Deposits are made up of numerous disseminated-type Deposits with low grades and small tonnages. They are linked to reef facies of Frasnian (=Upper Devonian) carbonate rocks. The largest exploited vein-type Deposits are hosted in Dinantian (=Lower Carboniferous) carbonate rocks. Lead isotopic studies reveal that the main primary source of the metals is in Middle and Upper Devonian sedimentary rocks. Hydrothermal solutions precipitated their metals at temperatures <180°C (110°C in the Verviers Synclinorium) and pressures of 108 Pa (<2×107 Pa in the Verviers Synclinorium). Salinities of the fluids were often between 10 and 23 equiv. wt.% NaCl. The origin of the vein-type Deposits is related to the migration of underground waters, likely gravity-driven, that leach the metals of the surrounding sedimentary rocks (mainly, those of Devonian age, after Pb isotopic data). The La Calamine paleokarstic Deposit was the largest Zn ore body in Belgium. It was continuously exploited from the 14th century up to 1884 and produced more than 600 000 tonnes of zinc metal. It was at La Calamine that the chemist Dony, from Liege, invented the first industrial process to transform the calamines into malleable zinc. This was patented by Napoleon I in 1810. Because Belgium occupies an area of the Variscan foreland between Germany and Ireland, a comparison between Deposits of these countries is performed. Belgian Zn–Pb syn-diagenetic Deposit are however of types different from the volcanogenic massive sulfide Deposits of Germany, as well as from the strata-bound lenses of Ireland. Prospecting by private companies during the past 50 years has increased the tonnage of reserves adjacent to known Deposits. Lithogeochemical prospecting, however, has not led to the discovery of new economic ore Deposits. The Chaudfontaine Stratiform Deposit, situated above a Frasnian biostrome, is the only recent drilling discovery.

Ronald George Eggins - One of the best experts on this subject based on the ideXlab platform.

  • modelling thickness in a Stratiform Deposit using joint simulation techniques
    2006
    Co-Authors: Ronald George Eggins
    Abstract:

    The estimated economic value of a Stratiform mineral Deposit is often very sensitive to the modelling of thickness in a conformable sequence of beds. A coregionalisation model of thickness expresses the assumed underlying spatial relationships of bedding thickness on a regional scale. Joint simulation of thickness directly models the cross-correlation of bedding thickness in such a model. Many of the current techniques of joint simulation are limited in the number of variables that can be simulated due to the multiplicative increase in processing times, based on the number of variables and number of samples simulated. To minimise processing times some methods make use of simplifying assumptions on the coregionalisation model. For example the Markov model, in which the dependence of one variable on the other is limited to the collocated data, would be unlikely to apply to the thickness of conformable bedding in a Stratiform Deposit. Transforming the thickness variables to remove correlation, simulating, and then back transforming to original data space offered a possible solution. The Minimum/Maximum Autocorrelation Factor (MAF) technique was chosen as one most likely to successfully decorrelate numbers of thickness variables, if the assumptions regarding a two-structure linear coregionalisation model were reasonably satisfied by the sampled data. The assumptions are that a simple intrinsic model of coregionalisation can represent both a lower correlation (‘noise’) component and a higher correlation (‘signal’) component of the modelled data. This implies that the final coregionalisation model (noise plus signal) is made up of linear combinations of a single basic structure at different spatial scales. In a number of previous applications, this had not proved to be a particularly restrictive requirement of the model. The decorrelated variables can be independently simulated, and back transformed twice; firstly using a MAF back-transformation to obtain correlated Gaussian variables, and finally to original data space. The McArthur River silver/lead/zinc Stratiform Deposit in the Northern Territory of Australia was chosen as the case study because it had many of the characteristics needed to test and evaluate the MAF technique in a typical Stratiform Deposit. The orebody model contained seventeen (17) mineralised units forming a conformable sequence which had varying thickness and degrees of mineralisation, and which had good continuity across the Deposit. Cross-correlation between the thicknesses of the seventeen stratigraphic units was significant. The Deposit was heavily folded in certain areas and true thickness of the bedding was calculated from drillhole log data, and used for the simulation studies. A simple unfolding algorithm was utilised to effectively flatten the Deposit to allow the application of 2-D simulation techniques. Drillhole intersections often did not contain the full stratigraphic sequence of beds due to a series of normal faults criss-crossing the Deposit. Therefore, incomplete data in the drillhole would need to be removed from the data set, or the number of beds in the joint simulation would need to be reduced, to utilise the MAF technique. A method was developed and validated for the generation of missing thicknesses at a sample point which removed the requirement to delete real incomplete sub-sets of the data when utilising MAF. Sequential Gaussian Simulation (SGS) was used to simulate the MAF decorrelated variables under the assumption that the multi-Gaussian assumptions held. Bedding surface simulations were generated by the addition of true thickness perpendicular to a basal reference surface. The 2-D joint simulations of thicknesses and surfaces were considered successful within a domain of the Deposit where drillholes were approximately perpendicular to bedding after unfolding. The univariate, bivariate and spatial statistics of the original thickness data were reproduced accurately in the joint simulation model, including the crossvariograms of original thickness; especially compared to those obtained using independent simulation of thickness. It was concluded that the techniques could be successfully applied to other Stratiform Deposits if the recommended validation steps were carried out. No further difficulties should be encountered in applying the method to 2-D joint simulation of grades in a Stratiform Deposit. The full 3-D joint simulation of variables in any Deposit using MAF would be assisted by the technique to generate missing variables at a point.

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

  • major and trace element geochemistry of pyrite and pyrrhotite from Stratiform and lamellar orebodies implications for the ore genesis of the dongguashan copper gold Deposit eastern china
    Minerals, 2018
    Co-Authors: Zhongfa Liu, Yongjun Shao, Haodi Zhou, Nan Liu, Kuanxin Huang, Qingquan Liu, Jiandong Zhang, Cheng Wang
    Abstract:

    The Dongguashan copper (gold) Deposit in Anhui Province is one of the largest copper (gold) Deposits in the Tongling ore district, which is the most important region in the Middle–Lower Yangtze River Metallogenic Belt, Eastern China. Stratiform and lamellar orebodies are the major Deposit types. Pyrite and pyrrhotite from the Stratiform Deposit type (Py I, Po I) and lamellar Deposit type (Py II, Po II) are investigated using Electron-probe Microanalyses (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Py I, Py II, Po I and Po II have high contents of Cu, Co, Au and Se, low contents of As, Pb and Zn, with Co/Ni ratios of 0.50−48.00, 4.00−45.00, 1.55−14.45 and 1.02−1.36, respectively, most of which are greater than 1 and vary widely; these characteristics are consistent with those of pyrite with a magmatic–hydrothermal origin. The higher Au/Ag and Fe/(S + As) ratios of pyrite and crystallization temperatures (286–387 °C) of hexagonal pyrrhotite indicate that the mineralization occurrs in environments with medium- to high-temperatures, high sulfur fugacity and medium-shallow depths. Therefore, we suggest that the Dongguashan copper (gold) Deposit is a stratabound skarn-type ore Deposit associated with magma intrusion activity during the Yanshanian Period.

Zhongfa Liu - One of the best experts on this subject based on the ideXlab platform.

  • major and trace element geochemistry of pyrite and pyrrhotite from Stratiform and lamellar orebodies implications for the ore genesis of the dongguashan copper gold Deposit eastern china
    Minerals, 2018
    Co-Authors: Zhongfa Liu, Yongjun Shao, Haodi Zhou, Nan Liu, Kuanxin Huang, Qingquan Liu, Jiandong Zhang, Cheng Wang
    Abstract:

    The Dongguashan copper (gold) Deposit in Anhui Province is one of the largest copper (gold) Deposits in the Tongling ore district, which is the most important region in the Middle–Lower Yangtze River Metallogenic Belt, Eastern China. Stratiform and lamellar orebodies are the major Deposit types. Pyrite and pyrrhotite from the Stratiform Deposit type (Py I, Po I) and lamellar Deposit type (Py II, Po II) are investigated using Electron-probe Microanalyses (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Py I, Py II, Po I and Po II have high contents of Cu, Co, Au and Se, low contents of As, Pb and Zn, with Co/Ni ratios of 0.50−48.00, 4.00−45.00, 1.55−14.45 and 1.02−1.36, respectively, most of which are greater than 1 and vary widely; these characteristics are consistent with those of pyrite with a magmatic–hydrothermal origin. The higher Au/Ag and Fe/(S + As) ratios of pyrite and crystallization temperatures (286–387 °C) of hexagonal pyrrhotite indicate that the mineralization occurrs in environments with medium- to high-temperatures, high sulfur fugacity and medium-shallow depths. Therefore, we suggest that the Dongguashan copper (gold) Deposit is a stratabound skarn-type ore Deposit associated with magma intrusion activity during the Yanshanian Period.

W. E. L. M•nter - One of the best experts on this subject based on the ideXlab platform.

  • Detrital Gold, Uranium, and Pyrite Concentrations Belated to Sedimentology in the Precambrian Vaal Beef Placer,
    2016
    Co-Authors: Witwatersrand South Africa, W. E. L. M•nter
    Abstract:

    The Vaal Reef placer was Deposited during the Vaal Stage of the Upper Witwaters-rand System, approximately 2,500 million years ago. The Stratiform Deposit is up to 5 feet thick and covers an area of over 100 square miles. It was discovered in 1934 and today is exploited at eight adjacent gold mines which produce approximately 16 percent of South Africa's total gold output. This study integrates stratigraphical, structural, petrological, and mineralogical data with a comprehensive set of sedimentological data to synthezise a model that describes the genesis of the Vaal Reef placer. Results show that the Vaal Reef placer was a shoreline feature of the Upper Witwatersrand Basin and that its Deposition was con-trolled, firstly, by the major structure of the basin and, secondly, by a minor transverse synclinal structure that induced an entry point. The sediments in the footwall of the Vaal Reef placer regressed into the Depository down a southeastern paleoslope in a shallow water fluviodeltaic environment. Lateral Depositional limits are evident. A reduced supply of sediment o the tectonically subsiding shoreline resulted in a trans