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1.
The Wangu gold deposit in northeastern Hunan, South China, is one of many structurally controlled gold deposits in the Jiangnan Orogen. The host rocks (slates of the Lengjiaxi Group) are of Neoproterozoic age, but the area is characterized by a number of Late Jurassic–Cretaceous granites and NE-trending faults. The timing of mineralization, tectonic setting and ore genesis of this deposit and many similar deposits in the Jiangnan Orogen are not well understood. The orebodies in the Wangu deposit include quartz veins and altered slates and breccias, and are controlled by WNW-trending faults. The principal ore minerals are arsenopyrite and pyrite, and the major gangue minerals are quartz and calcite. Alteration is developed around the auriferous veins, including silicification, pyritic, arsenopyritic and carbonate alterations. Field work and thin section observations indicate that the hydrothermal processes related to the Wangu gold mineralization can be divided into five stages: 1) quartz, 2) scheelite–quartz, 3) arsenopyrite–pyrite–quartz, 4) poly-sulfides–quartz, and, 5) quartz–calcite. The Lianyunshan S-type granite, which is in an emplacement contact with the NE-trending Changsha-Pingjiang fracture zone, has a zircon LA-ICPMS U–Pb age of 142 ± 2 Ma. The Dayan gold occurrence in the Changsha-Pingjiang fracture zone, which shares similar mineral assemblages with the Wangu deposit, is crosscut by a silicified rock that contains muscovite with a ca. 130 Ma 40Ar–39Ar age. The gold mineralization age of the Wangu deposit is thus confined between 142 Ma and 130 Ma. This age of mineralization suggests that the deposit was formed simultaneously with or subsequently to the development of NE-trending extensional faults, the emplacement of Late Jurassic–Cretaceous granites and the formation of Cretaceous basins filled with red-bed clastic rocks in northeastern Hunan, which forms part of the Basin and Range-like province in South China. EMPA analysis shows that the average As content in arsenopyrite is 28.7 atom %, and the mineralization temperature of the arsenopyrite–pyrite–quartz stage is estimated to be 245 ± 20 °C from arsenopyrite thermometry. The high but variable Au/As molar ratios (>0.02) of pyrite suggest that there are nanoparticles of native Au in the sulfides. An integration of S–Pb–H–O–He–Ar isotope systematics suggests that the ore fluids are mainly metamorphic fluids originated from host rocks, possibly driven by hydraulic potential gradient created by reactivation of the WNW-trending faults initially formed in Paleozoic, with possible involvement of magmatic and mantle components channeled through regional fault networks. The Wangu gold deposit shares many geological and geochemical similarities as well as differences with typical orogenic, epithermal and Carlin-type gold deposits, and may be better classified as an “intracontinental reactivation” type as proposed for many other gold deposits in the Jiangnan Orogen. 相似文献
2.
Several occurrences of gold-bearing quartz veins are situated along the east–northeast-trending Barramiya–Um Salatit ophiolitic belt in the central Eastern Desert of Egypt. In the Barramiya mine, gold mineralization within carbonaceous, listvenized serpentinite and adjacent to post-tectonic granite stocks points toward a significant role of listvenitization in the ore genesis. The mineralization is related to quartz and quartz–carbonate lodes in silicified/carbonatized wallrocks. Ore minerals, disseminated in the quartz veins and adjacent wallrocks are mainly arsenopyrite, pyrite and trace amounts of chalcopyrite, sphalerite, tetrahedrite, pyrrhotite, galena, gersdorffite and gold. Partial to complete replacement of arsenopyrite by pyrite and/or marcasite is common. Other secondary phases include covellite and goethite. Native gold and gold–silver alloy occur as tiny grains along micro-fractures in the quartz veins. However, the bulk mineralization can be attributed to auriferous arsenopyrite and arsenic-bearing pyrite (with hundreds of ppms of refractory Au), as evident by electron microprobe and LA-ICP-MS analyses.The mineralized quartz veins are characterized by abundant carbonic (CO2 ± CH4 ± H2O) and aqueous-carbonic (H2O–NaCl–CO2 ± CH4) inclusions along intragranular trails, whereas aqueous inclusions (H2O–NaCl ± CO2) are common in secondary sites. Based on the fluid inclusions data combined with thermometry of the auriferous arsenopyrite, the pressure–temperature conditions of the Barramiya gold mineralization range from 1.3 to 2.4 kbar at 325–370 °C, consistent with mesothermal conditions. Based on the measured δ34S values of pyrite and arsenopyrite intimately associated with gold, the calculated δ34SΣs values suggest that circulating magmatic, dilute aqueous-carbonic fluids leached gold and isotopically light sulfur from the ophiolitic sequence. As the ore fluids infiltrated into the sheared listvenite rocks, a sharp decrease in the fluid fO2 via interaction with the carbonaceous wallrocks triggered gold deposition in structurally favorable sites. 相似文献
3.
The Córrego do Sítio lineament is defined as a 16-km long, NE-SW-trending ductile shear zones, which controls fourteen gold deposits, including the Carvoaria Velha deposit. The dominant lithotypes of this deposit are metagrewackes with subordinate carbonaceous phyllites lenses of the Archean Rio das Velhas greenstone belt, which host gold mineralization. Metamafic dikes and sills are parallel and crosscut the host metasedimentary sequence. All these rocks exhibit alteration to quartz, carbonate and sericite, besides sulfides and sulfosalts. The main gold mineralization styles at the Carvoaria Velha deposit, and at Córrego do Sítio as a whole, are quartz-carbonate-sulfide ± sulfosalt veins of varied distribution. The veins are classified as: V1 veins – quartz-ankerite-pyrite-berthierite-gold – parallel to the main regional foliation Sn,; V2 veins – quartz-ankerite-pyrite – developed at extensional crenulation cleavage Sn + 1, and rarely gold mineralized; V3 veins – quartz-ankerite – filling Sn + 3 fractures, usually free of sulfides and sulfosalts; V4 veins – quartz-calcite – of restricted occurrence in metamafic dikes and sills. The latter crosscut the metasedimentary sequence, are extensional and display no preferential orientation. The most common ore minerals in all vein types are arsenopyrite, pyrite, berthierite, and pyrrhotite. Microprobe analyses reveal the presence of metallic phases rich in Sb, Pb and Co, such as stibnite, ullmanite, tetrahedrite, galena, cobaltite, which commonly overgrow the sulfides. Fluid inclusion studies trapped in quartz from V1, V2 and V4 veins have identified a H2O-CO2 ± CH4-NaCl mineralizing fluid that may contain KCl, MgCl2 e FeCl2. The presence of CH4 in fluid inclusions of the V1 and V2 veins reflect interaction of the fluid with the Córrego do Sítio and Santa Quitéria carbon-bearing metapelitic host units.Based on the microthermometric data, the hydrothermal fluid is interpreted to have evolved in at least two stages: i) an early fluid stage, trapped in smoky quartz, of moderate salinity (~ 8.5 eq. wt% NaCl), and minimal trapping temperature of 330 ± 17 °C; and ii) a late-stage fluid trapped in recrystallized quartz with lower salinity (~ 4.6 eq. wt% NaCl), and a minimal trapping temperature of 365 ± 33 °C. Isotopic values of δ18Ofluid (+ 7.9 and + 13.0‰), Δ33S (+ 0.3 to + 3.5‰) and δ34S (− 2.9 to + 6.1‰) suggest that indeed the hydrothermal fluid responsible for the gold mineralization at the Carvoaria Velha deposit must have had a metamorphic origin, and interacted with metasedimentary sequences during its ascending path. The addition of CH4 during fluid-rock interaction may have caused some decrease in ƒO2 of the fluid which, as a consequence, destabilized gold-bearing sulfur complexes, liberating S− 2 for the formation of Fe sulfides and sulfosalts (arsenopyrite, pyrite, pyrrothite and berthierite, etc.), and outcome gold deposition. 相似文献
4.
《Russian Geology and Geophysics》2015,56(10):1414-1427
The Ta Nang gold deposit is localized in Middle Jurassic black shales. The ore zone is a series of layer-by-layer crush zones and zones of hydrothermal rock alteration, < 10 m in thickness and > 2 km in length. It consists of quartz-sulfide veins, sulfidized black shales, and their hydrothermally altered varieties. Sulfide mineralization occurs as two assemblages: early pyrite-arsenopyrite and late chalcopyrite-sphalerite- galena. The pyrite-arsenopyrite assemblage is composed of different morphogenetic varieties. Coarse-crystalline arsenopyrite and pyrite aggregates and metacrystals of different orientations, 0.1 to 10 mm in size, are the most widespread. The chalcopyrite-sphalerite-galena assemblage is scarce. Along with the main ore minerals, it includes more rare minerals: pyrrhotite, lead sulfosalts (tsugaruite), and gold, which form a spatial assemblage with the main minerals or small inclusions in them. Gold occurs mainly as fine dissemination in cracks in pyrite, arsenopyrite, chalcopyrite, and quartz. Gold content in sulfidized carbonaceous shales is no more than tenths of ppm, averaging 0.38 ppm. This content in the quartz veins is considerably higher, averaging 3.92 ppm. Silver contents in the shales and quartz veins are similar and equal to 2.68 and 5.30 ppm, respectively. Also, the sulfidized rocks and veins have elevated contents of Fe, As, Pb, Zn, Cu, Cd, Ni, and Co; most of these elements (Fe, As, Pb, Zn, and Cu) make up their own sulfide minerals, and the others are trace elements. According to 39Ar/40Ar dating of sericite from the quartz-sulfide veins, their age is 129.3 ± 5.6 Ma, which is close to the age of the Cretaceous granite intrusions of the Deo Ca complex. These veins formed from moderately strong solutions (11.7-6.4 wt.% NaCl equiv) with the CH4 + N2 + CO2 gas phase at 340–130 °C. Judging from the S isotope composition (534S = 1.6-4.3%c), predominantly deep-seated endogenic sulfur participated in the formation of ore sulfide associations. Analysis of the distribution of gold shows that it was deposited together with sulfide minerals (galena, sphalerite, and chalcopyrite) at a later stage. 相似文献
5.
The world-class > 4 Moz Wona-Kona gold deposit is hosted within the Paleoproterozoic Birimian Houndé greenstone belt which is the most important gold mineralized belt in the western part of Burkina Faso, with a cumulative reserve of ~ 11 Moz. The mineralization consists of a pervasive silicification with disseminated pyrite–arsenopyrite crosscut by quartz–carbonate veinlets (1 to 10 cm wide) forming a vertical, thick (up to 40 m) and laterally extensive (5 km) northeast trending orebody hosted within a large (200 m wide) shear zone of regional extent. Gold occurs in association with 3 generations of pyrite and 2 generations of arsenopyrite. Free gold, interpreted as the last mineralizing event, occurs as late fracture filling in the pervasive silicification zone. 相似文献
6.
Vein-type gold deposits in the Atud area are related to the metagabbro–diorite complex that occurred in Gabal Atud in the Central Eastern Desert of Egypt. This gold mineralization is located within quartz veins and intense hydrothermal alteration haloes along the NW–SE brittle–ductile shear zone, as well as along the contacts between them. By using the mass balance calculations, this work is to determine the mass/volume gains and losses of the chemical components during the hydrothermal alteration processes in the studied deposits. In addition, we report new data on the mineral chemistry of the alteration minerals to define the condition of the gold deposition and the mineralizing fluid based on the convenient geothermometers. Two generations of quartz veins include the mineralized grayish-to-white old vein (trending NW–SE), and the younger, non-mineralized milky white vein (trending NE–SW). The ore minerals associated with gold are essentially arsenopyrite and pyrite, with chalcopyrite, sphalerite, enargite, and goethite forming during three phases of mineralization; first, second (main ore), and third (supergene) phases. Three main hydrothermal alteration zones of mineral assemblages were identified (zones 1–3), placed around mineralized and non-mineralized quartz veins in the underground levels. The concentrations of Au, Ag, and Cu are different from zone to zone having 25–790 ppb, 0.7–69.6 ppm, and 6–93.8 ppm; 48.6–176.1 ppb, 0.9–12.3 ppm, and 39.6–118.2 ppm; and 53.9–155.4 ppb, 0.7–3.4 ppm, and 0.2–79 ppm for zones 1, 2, and 3, respectively.The mass balance calculations and isocon diagrams (calculated using the GEOISO-Windows program) revealed the gold to be highly associated with the main mineralized zone as well as sericitization/kaolinitization and muscovitization in zone 1 more than in zones 2 and 3. The sericite had a higher muscovite component in all analyzed flakes (average XMs = 0.89), with 0.10%–0.55% phengite content in wall rocks and 0.13%–0.29% phengite content in mineralized quartz veins. Wall rocks had higher calcite (CaCO3) contents and lower MgCO3 and FeCO3 contents than the quartz veins. The chlorite flakes in the altered wall rocks were composed of pycnochlorite and ripidolite, with estimated formation temperatures of 289–295 °C and 301–312 °C, respectively. Albite has higher albite content (95.08%–99.20%) which occurs with chlorite in zone 3. 相似文献
7.
The giant Jianchaling gold deposit is located in the Shaanxi Province, China. The mineralization is hosted by WNW-trending faults in the Mianxian-Lueyang-Yangpingguan (MLY) area. The mineralization can be divided into three stages based on mineralogical assemblages and crosscutting relationships of mineralized quartz veins. These stages, from early to late, are characterized by the mineral assemblage of: (1) quartz – coarse-grained pyrite – pyrrhotite – pentlandite – dolomite; (2) quartz – pyrite – gold – sphalerite – galena – carbonate – arsenopyrite – fuchsite; and (3) dolomite – calcite – quartz – fine-grained pyrite – realgar – orpiment.Three types of fluid inclusions have been recognized in this study based on petrographic and microthermometric measurements, including pure CO2 and/or CH4 (PC-type), NaCl-H2O (W-type), and NaCl-CO2-H2O (C-type) fluid inclusions. These fluid inclusion types are present in quartz from the Stage 1 and 2 assemblages, whereas the Stage 3 quartz only contains W-type fluid inclusions. The Stage 2 assemblage is associated with the mineralization at the Jianchaling deposit. Fluid inclusions of Stage 1 quartz homogenize mainly between 250° and 360 °C, with salinities up to 15.6 wt.% NaCl equiv., whereas the Stage 3 dolomite with homogenization temperatures of 160° – 220 °C and salinities of 1.1–7.4 wt.% NaCl equiv. This indicates that the ore fluid system evolved from CO2-rich, probably metamorphic hydrothermal to CO2-poor, meteoric fluid. All three types of fluid inclusions can be observed in the Stage 2 quartz, suggesting that this heterogeneous association was trapped from a boiling fluid system. These inclusions homogenized at temperatures of 200°–250 °C and salinities of 1.2–12.4 wt.% NaCl equiv. The estimated trapping pressures of the fluid inclusions are between 117 and 354 MPa in Stage 1, suggesting an alternating lithostatic–hydrostatic fluid system, which was controlled by a fault-valve at the depth of ~ 12 km.Two fuchsite samples collected from the Stage 2 polymetallic-quartz veins yielded well-defined 40Ar/39Ar isotopic plateau ages of 197 ± 2 and 194 ± 2 Ma, and 39Ar/36Ar-40Ar/36Ar normal isochrones of 198 ± 2 and 199 ± 2 Ma. This indicates that the mineralization at Jianchaling is Early Jurassic (ca. 198 Ma) in age. We propose that Jianchaling is an orogenic gold deposit, and formed during continental collision related to the northward subduction of the Mian-Lue oceanic plate during the Early Jurassic. We also conclude that the beginning of the continental collision between the Yangtze and the North China Cratons took place around 200 Ma. 相似文献
8.
The Milin Kamak gold-silver deposit is located in Western Srednogorie zone, 50 km west of Sofia, Bulgaria. This zone belongs to the Late Cretaceous Apuseni-Banat-Timok-Srednogorie magmatic and metallogenic belt. The deposit is hosted by altered trachybasalt to andesitic trachybasalt volcanic and volcanoclastic rocks with Upper Cretaceous age, which are considered to be products of the Breznik paleovolcano. Milin Kamak is the first gold-silver intermediate sulfidation type epithermal deposit recognized in Srednogorie zone in Bulgaria. It consists of eight ore zones with lengths ranging from 400 to 1000 m, widths from several cm to 3–4 m, rarely to 10–15 m, an average of 80–90 m depth (a maximum of 200 m) and dip steeply to the south. The average content of gold is 5.04 g/t and silver – 13.01 g/t. The styles of alteration are propylitic, sericite, argillic, and advanced argillic. Ore mineralization consists of three stages. Quartz-pyrite stage I is dominated by quartz, euhedral to subhedral pyrite, trace pyrrhotite and hematite in the upper levels of the deposit. Quartz-polymetallic stage II is represented by major anhedral pyrite, galena, Fe-poor sphalerite; minor chalcopyrite, tennantite, bournonite, tellurides and electrum; and trace pyrrhotite, arsenopyrite, marcasite. Gangue minerals are quartz and carbonates. The carbonate-gold stage III is defined by deposition of carbonate minerals and barite with native gold and stibnite.Fluid inclusions in quartz are liquid H2O-rich with homogenization temperature (Th) ranging from 238 to 345 °C as the majority of the measurements are in the range 238–273 °C. Ice-melting temperatures (Tm) range from −2.2 to −4.1 °C, salinity – from 3.7 to 6.6 wt.% NaCl equiv. These measurements imply an epithermal environment and low- to moderate salinity of the ore-forming fluids.δ34S values of pyrite range from −0.49 to +2.44‰. The average calculated δ34S values are 1.35‰. The total range of δ34S values for pyrite are close to zero suggesting a magmatic source for the sulfur. 相似文献
9.
The Fairview and Sheba mines are two of the major gold mines in the Paleoarchean Barberton Greenstone Belt of Southern Africa. At these mines, gold is associated with quartz–carbonate ± rutile veins and occurs both as “invisible” gold finely dispersed in sulfides (primarily pyrite and arsenopyrite), and as visible electrum grains hosted in pyrite. Up to approximately 1000 ppm Au are contained in pyrite, and up to approximately 1700 ppm in arsenopyrite. Mapping of trace element distribution in sulfide minerals using electron microprobe and proton probe techniques revealed multiple events of ore formation and Au mineralisation. At Fairview mine, three stages of pyrite formation were identified, the last of which is associated with arsenopyrite, electrum and other sulfide minerals (sphalerite, chalcopyrite, galena, gersdorffite, and Sb-sulfides). At Sheba mine, pyrite was deposited in two stages, and electrum is associated with the second stage. At both mines, the last stage of sulfide formation is the main stage of Au deposition, and is associated with mobilisation of Au, As, Sb, Cu, Zn, and Ni. The host rock composition seems to have affected the composition of pyrite, since higher Ni and Co concentrations (up to 1.4 and 1.6 wt.%, respectively) have been measured in meta-(ultra)mafic host rocks in comparison with chert and metagreywacke. Arsenopyrite is chemically zoned, and has Sb- and S-rich cores and As- and Ni-rich rims. This zoning indicates variations in fluid compositions (decreasing Sb and increasing Ni), and crystallisation conditions (increasing As content for increasing temperature). Geothermometric estimates based on the As content of arsenopyrite (As ≤ 32 at.%) indicate temperatures up to ~ 420 °C for the crystal rims. Petrographic and cathodoluminescence observations of quartz associated with gold mineralisation show only local brittle deformation, and no plastic deformation. This supports the notion that the ore-transporting veins were emplaced late in the deformation history. Variations of cathodoluminescence of quartz are correlated with changing Al contents (Al ≤ 0.16 wt.%), and can be related to fluctuations in the pH of the mineralising fluids. 相似文献
10.
The Urals is a complex fold belt, which underwent long geological evolution. The formation of most gold deposits in the Urals is related to the collision stage. In this paper, we review some relatively small listvenite-related gold deposits, which are confined to the large Main Uralian fault zone and some smaller faults within the Magnitogorsk zone. The Mechnikovskoe, Altyn-Tash, and Ganeevskoe deposits are studied in detail in this contribution. They comprise the ore clusters along with other numerous small gold deposits, and constituted the sources for the gold placers exploited in historical time. The gold is hosted by metasomatites (listvenites, beresites) and quartz veins with economic gold grades (up to 20 g/t Au). Listvenites are developed after serpentinites and composed of quartz, fuchsite, and carbonates (magnesite, dolomite) ± albite. Volcanic and volcanoclastic rocks are altered to beresites, consisting of sericite, carbonates (dolomite, ankerite), quartz and albite. Pyrite and chalcopyrite are major ore minerals associated with gold; pyrrhotite, Ni sulfides, galena, sphalerite, arsenopyrite and Au-Ag tellurides are subordinate and rare. Gold in these deposits is mostly high-fineness (>900‰). The lower fineness (∼800‰) is typical of gold in assemblage with polymetallic sulfides and tellurides. The ores have been formed from the NaCl–CO2–H2O ± CH4 fluids of low (∼2 wt% NaCl-equiv.) to moderate (8–16 wt% NaCl-equiv.) salinity at temperatures of 210–330 °C. The oxygen isotopic composition of quartz (δ18O) varies from 14.7 to 15.4‰ (Mechnikovskoe deposit), 13.2 to 13.6‰ (Altyn-Tash deposit) and 12.0 to 12.7‰ (Ganeevskoe deposit). The oxygen isotopic composition of albite from altered rocks of the Ganeevskoe deposit is 10.1‰. The calculated δ18OH2O values of the fluid in equilibrium with quartz are in a range of 5.7–6.3, 4.2–4.6 and 6.3–6.7‰ respectively, and most likely indicate a magmatic fluid source. 相似文献
11.
Gold deposits in the Syama and Tabakoroni goldfields in southern Mali occur along a north-northeast trending mineralised litho-structural corridor that trends for approximately 40 km. The deposits are interpreted to have formed during a craton-wide metallogenic event during the Eburnean orogeny. In the Syama goldfield, gold mineralisation in 9 deposits is hosted in the hanging-wall of the Syama-Bananso Shear Zone in basalt, greywacke, argillite, lamprophyre, and black shale. Gold is currently mined primarily from the oxidised-weathered zone of the ore bodies. In the Syama deposit, mineralisation hosted in altered basalt is associated with an intense ankerite–quartz–pyrite stockwork vein systems, whereas disseminated style mineralisation is also present in greywackes. In contrast, the Tellem deposit is hosted in quartz–porphyry rocks.In the Tabakoroni goldfield, gold mineralisation is hosted in quartz veins in tertiary splay shears of the Syama-Bananso Shear Zone. The Tabakoroni orebody is associated with quartz, carbonate and graphite (stylolite) veins, with pyrite and lesser amounts of arsenopyrite. There are four main styles of gold mineralisation including silica-sulphide lodes in carbonaceous fault zones, stylolitic quartz reefs in fault zones, quartz–Fe–carbonate–sulphide lodes in mafic volcanics, and quartz–sulphide stockwork veins in silicified sediments and porphyry dykes. The several deposit styles in the goldfield thus present a number of potential exploration targets spatially associated with the regional Syama-Bananso Shear Zone and generally classified as orogenic shear-hosted gold deposits. 相似文献
12.
The Dongping gold deposit hosted in syenites is one of the largest hydrothermal gold deposits in China and composed of ore veins in the upper parts and altered zones in the lower parts of the ore bodies. Pervasive potassic alteration and silicification overprint the wall rocks of the ore deposit. The alteration minerals include orthoclase, microcline, perthite, quartz, sericite, epidote, calcite, hematite and pyrite, with the quartz, pyrite and hematite assemblages closely associated with gold mineralization. The phases of hydrothermal alteration include: (i) potassic alteration, (ii) potassic alteration - silicification, (iii) silicification - epidotization - hematitization, (iv) silicification - sericitization - pyritization and (v) carbonation. Mass-balance calculations in potassic altered and silicified rocks reveal the gain of K2O, Na2O, SiO2, HFSEs and transition elements (TEs) and the loss of REEs. Most major elements were affected by intense mineral reactions, and the REE patterns of the ore are consistent with those of the syenites. Gold, silver and tellurium show positive correlation and close association with silicification. Fluid inclusion homogenization temperatures in quartz veins range from 154 °C to 382 °C (peak at 275 °C–325 °C), with salinities of 4–9 wt.% NaCl equiv. At temperatures of 325 °C the fluid is estimated to have pH = 3.70–5.86, log fO2 = − 32.4 to − 28.1, with Au and Te transported as Au (HS)2− and Te22 − complexes. The ore forming fluids evolved from high pH and fO2 at moderate temperatures into moderate-low pH, low fO2 and low temperature conditions. The fineness of the precipitated native gold and the contents of the oxide minerals (e.g., magnetite and hematite) decreased, followed by precipitation of Au- and Ag-bearing tellurides. The hydrothermal system was derived from an alkaline magma and the deposit is defined as an alkaline rock-hosted hydrothermal gold deposit. 相似文献
13.
The Inata gold deposit is hosted in the Bouroum greenstone belt of northern Burkina Faso and contains ca. 5 Moz of gold resource. The greenstone belt is divided into 4 distinct domains: The Pali West, Pali-Minfo and Fété Kolé domains comprised of variable proportions of mafic to intermediated volcanic, volcaniclastic and sedimentary rocks, and the Sona Basin comprised of feldspathic sandstones and turbidites. Potential Tarkwaian-like conglomerates are rarely observed on the eastern margin of the basin. The stratigraphy is crosscut by a series of intrusions between 2172 ± 15 Ma and 2122 ± 4 Ma. A complex deformation sequence is recorded in the rocks and has been interpreted in a five stage scheme: early syn-depositional basin margin faults reactivated through time and partitioning all subsequent regional deformation (DeB); N–S compression (D1B > 2172 Ma); E-W compression (D2B, < ca 2122 Ma); NW–SE compression (D3B), and a late N–S compression (D4B). D2B-D4B overprint all rocks, including those of the Sona Basin and Tarkwaian-like conglomerates. Peak metamorphism is mid- to upper-greenschist facies.Mineralisation at Inata is hosted in black shales and volcaniclastic rocks of the Pali-Minfo domain and comprises shear-zone hosted quartz-tourmaline-ankerite veins with associated sulphides dominated by pyrite and arsenopyrite. Three generations of pyrite (py1, py2, py3) and one generation of arsenopyrite (apy2) have been identified. Py1 is parallel to bedding and early D1B foliation and not associated with gold. Py2 and apy2 are coeval, contain up to 1 ppm gold and are spatially associated with auriferous quartz veins. Py3 locally overprints previous assemblages and is also associated with Au. Fluid inclusions in quartz indicate H2O to H2O–CO2–NaCl fluids in auriferous quartz veins.Microscopic to macroscopic observation of fabric-mineral-vein crosscutting relationships indicate that mineralisation is syn-D2B, disrupted and remobilised during D3B. All observations and data are consistent with Inata representing an orogenic style of gold mineralisation formed relatively late in the evolution of the host terrane. 相似文献
14.
《Journal of African Earth Sciences》2008,50(2-4):204-214
The Tamlalt–Menhouhou gold deposit belongs to the Neoproterozoic–Palaeozoic Tamlalt inlier located in the Eastern High-Atlas (Morocco). It occurs in altered Upper Neoproterozoic bimodal volcanic and volcano-sedimentary units outcropping in the Tamlalt–Menhouhou area. Gold mineralization has been identified in quartz veins related to shear-zones associated with a strong quartz-phyllic-argillic alteration. Visible free gold is related to goethite–malachite–barite boxworks in quartz veins. The other alteration minerals accompanying gold mineralization are mainly carbonates, chlorite, hematite, albite and pyrite whose relative proportion defines three alteration types. 40Ar/39Ar geochronology performed on phengite grains from phyllic alteration and the auriferous quartz veins, yields plateau ages ranging from 300 ± 5 Ma to 284 ± 12 Ma with a weighted mean age of 293 ± 7 Ma. This identifies a Late Variscan age for the Tamlalt–Menhouhou “shear zones-related” gold deposit and emphasizes the consequences of the Variscan orogeny for gold mineralization in the High-Atlas and Anti-Atlas Neoproterozoic inliers. 相似文献
15.
The Sandaowanzi epithermal gold deposit (0.5 Moz or ca. 14 tons), located at the northern edge of the Great Xing'an range, NE China, is unique in that nearly all the gold (> 95%) is contained in gold tellurides mostly in bonanza grade ore shoots (the highest grade being up to 20,000 g/t). The bonanza ores are hosted in the central parts of large-scale (> 3 m wide, 200 m long) quartz veins which crosscut Early Cretaceous andesitic trachyte and trachytic andesite, and are, in turn, crosscut by diabase dykes of similar age. There are two ore types: low-grade disseminated ores and high-grade vein ores. In the former, very fine grains of Ag-rich tellurides (mainly hessite and petzite) coexist with sulfides (pyrite, sphalerite, galena and chalcopyrite), occurring as disseminated grains or sometimes as grain aggregates. In the high-grade vein ores, coarse-grained Au–(Ag)–tellurides (calaverite, sylvanite, krennerite, and petzite) form a major part of quartz–telluride veins. Chalcopyrite forms separate monomineralic veins emplaced within the quartz–telluride veins. Spectacular textures among coarse-grained (up to 3 cm in diameter) tellurides, and micron-scale bamboo shoot-like grains are observed. Two- and three-phase telluride symplectites are common in the vein ores.Fluid inclusion studies suggest that the mineralizing fluids are a mixture of magmatic and meteoric fluids, that homogenized in the temperature range of 260–280 °C. Sulfur isotope compositions of pyrite and chalcopyrite (δ34S − 1.64 to 1.91‰) support the origin of fluids from a deep source. It is suggested that faulting, temperature changes and variation in fS2 and fTe2 were major factors contributing to the two main types of mineralization and the differences between them. Early rapid cooling and subsequent slow cooling of the later fluids along fault and fracture zones were instrumental in formation of the two superposed ore types. Open-space filling and crack-sealing along fractures predominates over replacement during telluride mineralization. The Sandaowanzi deposit is a unique bonanza-grade accumulation of gold tellurides genetically related to subalkaline magmatism, which was genetically associated with Early Cretaceous regional extension. 相似文献
16.
Gold Mineralization of the Gatsuurt Deposit in the North Khentei Gold Belt,Central Northern Mongolia
Mineral assemblages, chemical compositions of ore minerals, wall rock alteration and fluid inclusions of the Gatsuurt gold deposit in the North Khentei gold belt of Mongolia were investigated to characterize the gold mineralization, and to clarify the genetic processes of the ore minerals. The gold mineralization of the deposit occurs in separate Central and Main zones, and is characterized by three ore types: (i) low‐grade disseminated and stockwork ores; (ii) moderate‐grade quartz vein ores; and (iii) high‐grade silicified ores, with average Au contents of approximately 1, 3 and 5 g t?1 Au, respectively. The Au‐rich quartz vein and silicified ore mineralization is surrounded by, or is included within, the disseminated and stockwork Au‐mineralization region. The main ore minerals are pyrite (pyrite‐I and pyrite‐II) and arsenopyrite (arsenopyrite‐I and arsenopyrite‐II). Moderate amounts of galena, tetrahedrite‐tennantite, sphalerite and chalcopyrite, and minor jamesonite, bournonite, boulangerite, geocronite, scheelite, geerite, native gold and zircon are associated. Abundances and grain sizes of the ore minerals are variable in ores with different host rocks. Small grains of native gold occur as fillings or at grain boundaries of pyrite, arsenopyrite, sphalerite, galena and tetrahedrite in the disseminated and stockwork ores and silicified ores, whereas visible native gold of variable size occurs in the quartz vein ores. The ore mineralization is associated with sericitic and siliceous alteration. The disseminated and stockwork mineralization is composed of four distinct stages characterized by crystallization of (i) pyrite‐I + arsenopyrite‐I, (ii) pyrite‐II + arsenopyrite‐II, (iii) galena + tetrahedrite + sphalerite + chalcopyrite + jamesonite + bournonite + scheelite, and iv) boulangerite + native gold, respectively. In the quartz vein ores, four crystallization stages are also recognized: (i) pyrite‐I, (ii) pyrite‐II + arsenopyrite + galena + Ag‐rich tetrahedrite‐tennantite + sphalerite + chalcopyrite + bournonite, (iii) geocronite + geerite + native gold, and (iv) native gold. Two mineralization stages in the silicified ores are characterized by (i) pyrite + arsenopyrite + tetrahedrite + chalcopyrite, and (ii) galena + sphalerite + native gold. Quartz in the disseminated and stockwork ores of the Main zone contains CO2‐rich, halite‐bearing aqueous fluid inclusions with homogenization temperatures ranging from 194 to 327°C, whereas quartz in the disseminated and stockwork ores of the Central zone contains CO2‐rich and aqueous fluid inclusions with homogenization temperatures ranging from 254 to 355°C. The textures of the ores, the mineral assemblages present, the mineralization sequences and the fluid inclusion data are consistent with orogenic classification for the Gatsuurt deposit. 相似文献
17.
The Wangfeng gold deposit is located in Western Tian Shan and the central section of the Central Asian Orogenic Belt (CAOB). The deposit is mainly hosted in Precambrian metamorphic rocks and Caledonian granites and is structurally controlled by the Shenglidaban ductile shear zone. The gold orebodies consist of gold-bearing quartz veins and altered mylonite. The mineralization can be divided into three stages: quartz–pyrite veins in the early stage, sulfide–quartz veins in the middle stage, and quartz–carbonate veins or veinlets in the late stage. Ore minerals and native gold mainly formed in the middle stage. Four types of fluid inclusions were identified based on petrography and laser Raman spectroscopy: CO2–H2O inclusions (C-type), pure CO2 inclusions (PC-type), NaCl–H2O inclusions (W-type), and daughter mineral-bearing inclusions (S-type). The early-stage quartz contains only primary CO2–H2O fluid inclusions with salinities of 1.62 to 8.03 wt.% NaCl equivalent, bulk densities of 0.73 to 0.89 g/cm3, and homogenization temperatures of 256 °C–390 °C. Vapor bubbles are composed of CO2. The middle-stage quartz contains all four types of fluid inclusions, of which the CO2–H2O and NaCl–H2O types yield homogenization temperatures of 210 °C–340 °C and 230 °C–300 °C, respectively. The CO2–H2O fluid inclusions have salinities of 0.83 to 9.59 wt.% NaCl equivalent and bulk densities of 0.77 to 0.95 g/cm3, with vapor bubbles composed of CO2, CH4, and N2. Fluid inclusions in the late-stage quartz are NaCl–H2O solution with low salinities (0.35–3.87 wt.% NaCl equivalent) and low homogenization temperatures (122 °C–214 °C). The coexistence of inclusions of these four types in middle-stage quartz suggests that fluid boiling occurred in the middle-stage mineralization. Trapping pressures estimated from CO2–H2O inclusions are 110–300 MPa and 90–250 MPa for the early and middle stages, respectively, suggesting that gold mineralization mainly occurred at depths of about 10 km. In general, the Wangfeng gold deposit originated from a metamorphic fluid system characterized by low salinity, low density, and enrichment of CO2. Depressurized fluid boiling caused gold precipitation. Given the regional geology, ore geology, fluid-inclusion features, and ore-forming age, the Wangfeng gold deposit can be classified as a hypozonal orogenic gold deposit. 相似文献
18.
《Ore Geology Reviews》2010,37(4):333-349
Gold mineralization at Jonnagiri, Dharwar Craton, southern India, is hosted in laminated quartz veins within sheared granodiorite that occur with other rock units, typical of Archean greenstone–granite ensembles. The proximal alteration assemblage comprises of muscovite, plagioclase, and chlorite with minor biotite (and carbonate), which is distinctive of low- to mid-greenschist facies. The laminated quartz veins that constitute the inner alteration zone, contain muscovite, chlorite, albite and calcite. Using various calibrations, chlorite compositions in the inner and proximal zones yielded comparable temperature ranges of 263 to 323 °C and 268 to 324 °C, respectively. Gold occurs in the laminated quartz veins both as free-milling native metal and enclosed within sulfides. Fluid inclusion microthermometry and Raman spectroscopy in quartz veins within the sheared granodiorite in the proximal zone and laminated auriferous quartz veins in inner zone reveal the existence of a metamorphogenic aqueous–gaseous (H2O–CO2–CH4 + salt) fluid that underwent phase separation and gave rise to gaseous (CO2–CH4), low saline (~ 5 wt.% NaCl equiv.) aqueous fluids. Quartz veins within the mylonitized granodiorites and the laminated veins show broad similarity in fluid compositions and P–T regime. Although the estimated P–T range (1.39 to 2.57 kbar at 263 to 323 °C) compare well with the published P–T values of other orogenic gold deposits in general, considerable pressure fluctuation characterize gold mineralization at Jonnagiri. Factors such as fluid phase separation and fluid–rock interaction, along with a decrease in f(O2), were collectively responsible for gold precipitation, from an initial low-saline metamorphogenic fluid. Comparison of the Jonnagiri ore fluid with other lode gold deposits in the Dharwar Craton and major granitoid-hosted gold deposits in Australia and Canada confirms that fluids of low saline aqueous–carbonic composition with metamorphic parentage played the most dominant role in the formation of the Archean lode gold systems. 相似文献
19.
紫木凼金矿床载金矿物及金的赋存状态 总被引：2，自引：0，他引：2
紫木凼金矿床主要载金矿物为含砷黄铁矿和毒砂,氧化矿石中,金呈显微粒状自然金－显微金嵌布于褐铁矿,石英水云母,方解石的颗粒间或孔隙中,原生矿石中,金主要呈次显微粒自然金－次显微金包裹体,其次是类质同像形式赋存在含砷黄铁矿和毒砂矿物中。 相似文献
20.
《Ore Geology Reviews》2008,33(3-4):629-650
In the Raposos orogenic gold deposit, hosted by banded iron-formation (BIF) of the Archean Rio das Velhas greenstone belt, the hanging wall rocks to BIF are hydrothermally-altered ultramafic schists, whereas metamafic rocks and their hydrothermal schistose products represent the footwall. Planar and linear structures at the Raposos deposit define three ductile to brittle deformational events (D1, D2 and D3). A fourth group of structures involve spaced cleavages that are considered to be a brittle phase of D3. The orebodies constitute sulfide-bearing D1-related shear zones of BIF in association with quartz veins, and result from the sulfidation of magnetite and/or siderite. Pyrrhotite is the main sulfide mineral, followed by lesser arsenopyrite and pyrite. At level 28, the hydrothermal alteration of the mafic and ultramafic wall rocks enveloping BIF define a gross zonal pattern surrounding the ore zones. Metabasalt comprises albite, epidote, actinolite and lesser Mg/Fe–chlorite, calcite and quartz. The incipient stage includes the chlorite and chlorite-muscovite alteration zone. The least-altered ultramafic schist contains Cr-bearing Mg-chlorite, actinolite and talc, with subordinate calcite. The incipient alteration stage is subdivided into the talc–chlorite and chlorite–carbonate zone. For both mafic and ultramafic wall rocks, the carbonate–albite and carbonate–muscovite zones represent the advanced alteration stage.Rare earth and trace element analyses of metabasalt and its alteration products suggest a tholeiitic protolith for this wall rock. In the case of the ultramafic schists, the precursor may have been peridotitic komatiite. The Eu anomaly of the Raposos BIF suggests that it was formed proximal to an exhalative hydrothermal source on the ocean floor. The ore fluid composition is inferred by hydrothermal alteration reactions, indicating it to having been H2O-rich containing CO2 + Na+ and S. Since the distal alteration halos are dominated by hydrated silicate phases (mainly chlorite), with minor carbonates, fixation of H2O is indicated. The CO2 is consumed to form carbonates in the intermediate alteration stage, in halos around the chlorite-dominated zones. These characteristics suggest variations in the H2O to CO2-ratio of the sulfur-bearing, aqueous-carbonic ore fluid, which interacted at varying fluid to rock ratios with progression of the hydrothermal alteration. 相似文献