Geology and mineralization of the Uchkoshkon tin deposit associated with a breccia pipe, Eastern Kyrgyzstan
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Abstract A primary deposit of tin and tungsten has been discovered in association with granites of the Cambrian (?) sub-volcanic igneous complex at Sabaloka, on the Nile north of Khartoum. Wolfram and cassiterite occur in a stockwork of quartz veins which also contain minor amounts of sulphide minerals. The stockwork centres around a small intrusion of primary greisen lying on the contact of a porphyritic microgranite ring-dyke but the greisen and mineralizing solutions are believed to have originated from a nearby mass of biotite-muscovite granite. The deposit has many features in common with the primary tin veins associated with the Younger Granites of northern Nigeria and other parts of northern Africa.
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Topaz
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ABSTRACT Gosowong province has economic mineralisation which is classified as low sulphidation epithermal veining system containing high-grade of gold and silver. It is characterizes by various veins hosted in Holocene Quaternary volcanic rocks, mineralisation generally occurs in host rock andesite. The Kencana epithermal vein system in Gosowong Au-Ag district hosted by two main sub-parallel North-West trending major fault structures, named Kencana One (K1) and Kencana Two (K2) with strike lenght extend up to 600m. Both structures joined by link structures, appears to be Kencana Link (K-Link) as the thickest link structure. The Kencana One (K1) is the first underground mine in Gosowong district. The nature of underground conditions at Kencana has a high variability of gold grades. Thus due to extremely high grades ore in Kencana, it is need to be precise and thoroughly handling to obtain best results. Primary mineralisation occurs in multistage veins, breccias and stockwork veins as infill structures. This study confirming that there is a strong correlation between quartz vein infill structure mode versus gold grade which classified into (1) 1.01-3.0g/t Au, dominated with wall-rock breccia and stockwork, (2) 3.01-6.0g/t Au, dominated with wall-rock breccia follows by stockwork, (3) 6.01-20.0g/t Au, dominated with wall-rock breccia follows by quartz lode and stockwork, (4) 20.01-80.0g/t Au, dominated by wall-rock breccia follows by vein breccia and quartz lode, (5) >80g/t Au, dominated by wall-rock breccia. In terms of production quartz vein infill mode together and quartz vein texture with gold grade has been used as the main reference for geologist to make a direction in the process of ore drive determination in underground mining operations. Keywords: Kencana, low sulphidation epithermal, quartz vein infill mode SARI Gosowong memiliki mineralisasi ekonomis yang merupakan epitermal sulfida rendah yang mengandung emas dan perak dengan kadar tinggi. Cebakan dicirikan dengan kehadiran urat yang bervariasi dengan batuan vulkanik kuarter sebagai batuan induk berumur Holosen, mineralisasi umumnya terjadi di dalam batuan induk andesit. Kencana berada di dalam area Cebakan Au-Ag Gosowong. Kencana terdiri dari dua struktur besar yang berdampingan, dinamakan Kencana Satu (K1) dan Kencana Dua (K2) dengan arah jurus sepanjang 600m. Keduanya dihubungkan dengan struktur yang dinamakan Kencana Link (K-Link) yang merupakan struktur bukaan yang paling tebal. K1 adalah tambang bawah tanah pertama di Gosowong. Kondisi bawah tanah di Kencana menunjukkan variasi tubuh bijih emas yang mengandung kadar emas yang bervariasi. Dengan adanya kadar emas yang tinggi, maka penangannya harus tepat dan seksama untuk mendapatkan hasil terbaik. Secara umum mineralisasi terjadi secara bertahap dalam urat kuarsa, breksiasi, dan urat stockwork. Penelitian ini menegaskan bahwa terdapat korelasi yang kuat antara tipe struktur urat kuarsa dengan kadar emas yang diklasifikasikan menjadi (1) 1 . 01-3.0 g/t Au, didominasi oleh breksiasi batuan dinding dan stockwork, (2) 3.01-6.0 g/t Au, didominasi oleh breksiasi batuan dinding diikuti oleh stockwork, (3) 6.01-20.0 g/t Au, didominasi oleh breksiasi batuan dinding diikuti oleh quartz lode dan stockwork (4) 20.01-80.0 g/t Au, didominasi oleh breksiasi batuan dinding diikuti oleh breksiasi urat kuarsa dan quartz lode (5) > 80g/t Au, didominasi oleh breksiasi batuan dinding. Di dalam proses produksi, tipe struktur urat kuarsa dan tekstur urat kuarsa bersama dengan kadar emas menjadi petunjuk untuk geolog dalam menentukan arah penambangan emas di dalam tambang bawah tanah. Kata kunci: epitermal sulfida rendah, Kencana, tipe struktur urat kuarsa
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The Baid al Jimalah tungsten deposit flat 25°09 N., long 42°41' E.) is a swarm of steeply dipping, sheeted, tungsten-bearing quartz veins. It is spatially, temporally, and genetically associated with a 569 Ma, highly differentiated, porphyritic granite that intrudes late Proterozoic, immature sandstones of the Murdama group. The bulk of the vein constituents came from hydrothermal fluids exsolved from a granite cupola at a depth of about 3.1 km during a single cycle of magma intrusion and hydrothermal mineralization. Hypogene mineralization can be divided into 3 main periods: early quartz-molybdenite stockwork veins, wolframite- and scheelite-bearing greisen veins, and late, barren veins. Each of the three periods can be divided into several stages that are transitional to each other. The greisen veins, in particular, show replacement of earlier mineral assemblages by later ones. The veins at Baid al Jimalah East, approximately 1.5 km to the east of the Baid al Jimalah tungsten deposit, are genetically related to it and probably formed while the greisen mineralization was being deposited. Early stockwork mineralization was formed near magmatic temperatures (580°-700°C) from low salinity fluids (1-2 weight percent NaCl equivalent). Two fluids were present, one low density and CO2 rich, the other high density and H2O rich. Greisen mineralization was formed from fluids in the liquid state at temperatures mostly between 390° and 430°C with salinities between 4.5 and 10.9 weight percent NaCl equivalent. Late, barren mineralization formed from liquids with salinities between 0.5 and 3.0 weight percent NaCl equivalent and at temperatures at least as low as 238°C. The veins at Baid al Jimalah East formed from liquids between 0 and 4.2 weight percent NaCl equivalent at temperatures largely between 300° and 375°C. Depth of mineralization was greater than 3.1 km. The temperatures given above have been corrected for pressure assuming this depth, and are 75-80°C higher than the fluid inclusion filling temperatures. Important volatile constituents of the hydrothermal fluids were CO2 and CH4, in addition to H2O and HF. Baid al Jimalah is similar in character and origin to other tungsten-tin greisen deposits in the world, especially the Hemerdon deposit in Devon, England. It is also analogous to Climax-type molybdenum deposits, which contain virtually identical mineral assemblages, but with the relative intensities of the molybdenum and tungsten mineralization reversed.
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Wolframite
Scheelite
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Topaz
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Abstract The Chehugou Mo–Cu deposit, located 56 km west of Chifeng, NE China, is hosted by Triassic granite porphyry. Molybdenite–chalcopyrite mineralization of the deposit mainly occurs as veinlets in stockwork ore and dissemination in breccia ore, and two ore‐bearing quartz veins crop out to the south of the granite porphyry stock. Based on crosscutting relationships and mineral paragenesis, three hydrothermal stages are identified: (i) quartz–pyrite–molybdenite ± chalcopyrite stage; (ii) pyrite–quartz ± sphalerite stage; and (iii) quartz–calcite ± pyrite ± fluorite stage. Three types of fluid inclusions in the stockwork and breccia ore are recognized: LV, two‐phase aqueous inclusions (liquid‐rich); LVS, three‐phase liquid, vapor, and salt daughter crystal inclusions; and VL, two‐phase aqueous inclusions (gas‐rich). LV and LVS fluid inclusions are recognized in vein ore. Microthermometric investigation of the three types of fluid inclusions in hydrothermal quartz from the stockwork, breccia, and vein ores shows salinities from 1.57 to 66.75 wt% NaCl equivalents, with homogenization temperatures varying from 114°C to 550°C. The temperature changed from 282–550°C, 220–318°C to 114–243°C from the first stage to the third stage. The homogenization temperatures and salinity of the LV, LVS and VL inclusions are 114–442°C and 1.57–14.25 wt% NaCl equivalent, 301–550°C and 31.01–66.75 wt% NaCl equivalent, 286–420°C and 4.65–11.1 wt% NaCl equivalent, respectively. The VL inclusions coexist with the LV and LVS, which homogenize at the similar temperature. The above evidence shows that fluid‐boiling occurred in the ore‐forming stage. δ 34 S values of sulfide from three type ores change from −0.61‰ to 0.86‰. These δ 34 S values of sulfide are similar to δ 34 S values of typical magmatic sulfide sulfur (c. 0‰), suggesting that ore‐forming materials are magmatic in origin.
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Breccia
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The Potosi primary tin deposit is an exogreisen body contained within a near vertical breccia pipe, related to a nearby Rondonian tin-granite. Its spacial position appears to have been controlled by prominent fractures in the basement through which the granite and orebody were intruded. Different types of greisen have been recognized in the field which correspond to greater or lesser metasomatic alteration of the gneiss breccia fragments. Topazite forms the breccia matrix. It is believed that the Potosi orebody formed as result of volatile concentration (particularly f1uorine) beneath an impermeable carapace of the Pedra Branca granite and the subsequent escape of these volatiles along the basement fractures to surface, producing the breccia and tin/tungsten mineralization.
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The Echassières district in central France contains complex rare-element ore deposits, whose formation is related to exotic igneous events and several hydrothermal episodes that are not entirely understood to date. Tungsten mineralization consists of three generations of wolframite, characterized by distinct Fe/Mn ratios (8.4; 3.5 and 0.3, for wolframite a, b and c, respectively), formed during three separate hydrothermal episodes related to the Variscan orogeny. Wolframite a occurs in quartz veins of the La Bosse stockwork where it crystallized before the Barrovian metamorphism that affected these veins and the host rock. After metamorphism, before intrusion of the Beauvoir and Colettes granites, wolframite b crystallized in the stockwork during massive topazification. High concentrations of wolframite c occur in the proximal quartz veins in the Mazet area, while only scant amounts are found in the La Bosse stockwork. In both settings, wolframite c precipitated from the fluid responsible for greisen alteration that massively affected the Beauvoir granite. In the La Bosse stockwork, greisen alteration is characterized by hydrothermal topaz that is texturally and chemically distinct from that precipitated during topazification. Supergene alteration responsible for kaolinization of Beauvoir and Colettes granites caused remobilization of a non-negligible amount of tungsten (W) during replacement of wolframite by W-rich goethite in all units of the Echassières district. This model for multiple W mineralizing events is novel and can prove essential in distinguishing potential economic deposits worldwide.
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Stockwork
Greisen
Topaz
Cassiterite
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Alunite
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Post-Delhi acid magmatism at Degana has yielded three intrusive bodies of topaz granite, the earliest one emplaced within phyllite of Delhi Supergroup and the other two successively in the core of previous intrusive, along with two generations of aplites. Wolframite mineralisation has occurred at two different stages during the magmatism: (1) greisen-bordered vein-type ore bodies hosted by the earliest granite intrusive and adjoining phyllite rcpresent the first stage, and (2) stockwork ore bodies hosted by an intrusion breecia developed at a later stage following the emplacement of other two granite bodies. Presence of topaz, Li-mica and fluorite is a characteristic feature of these granites and wolframite deposits. The granites are strongly peraluminous and geochemically specialised with enrichment of Li, F, Rb and depleted in Sr, K-As dating of zinnwaldite from wolframite bearing lode indicates an age of 860±25 Ma.
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