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1.
Gold mineralization at Hutti is confined to a series of nine parallel, N–S to NNW–SSE trending, steeply dipping shear zones.
The host rocks are amphibolites and meta-rhyolites metamorphosed at peak conditions of 660±40°C and 4±1 kbar. They are weakly
foliated (S1) and contain barren quartz extension veins. The auriferous shear zones (reefs) are typically characterized by four alteration
assemblages and laminated quartz veins, which, in places, occupy the entire reef width of 2–10 m, and contain the bulk of
gold mineralization. A <1.5 m wide distal chlorite-sericite (+biotite, calcite, plagioclase) alteration zone can be distinguished
from a 3–5 m wide proximal biotite-plagioclase (+quartz, muscovite, calcite) alteration zone. Gold is both spatially and temporally
associated with disseminated arsenopyrite and pyrite mineralization. An inner chlorite-K-feldspar (+quartz, calcite, scheelite,
tourmaline, sphene, epidote, sericite) alteration halo, which rims the laminated quartz veins, is characterized by a pyrrhotite,
chalcopyrite, sphalerite, ilmenite, rutile, and gold paragenesis. The distal chlorite-sericite and proximal biotite-plagioclase
alteration assemblages are developed in microlithons of the S2–S3 crenulation cleavage and are replaced along S3 by the inner chlorite-K-feldspar alteration, indicating a two-stage evolution for gold mineralization. Ductile D2 shearing, alteration, and gold mineralization formed the reefs during retrograde evolution and fluid infiltration under upper
greenschist to lower amphibolite facies conditions (560±60°C, 2±1 kbar). The reefs were reactivated in the D3 dextral strike-slip to oblique-slip environment by fault-valve behavior at lower greenschist facies conditions (ca. 300–350°C),
which formed the auriferous laminated quartz veins. Later D4 crosscutting veins and D5 faults overprint the gold mineralization. The alteration mineralogy and the structural control of the deposit clearly points
to an orogenic style of gold mineralization, which took place either during isobaric cooling or at different levels of the
Archean crust. From overlaps in the tectono-metamorphic history, it is concluded that gold mineralization occurred during
two tectonic events, affecting the eastern Dharwar craton in south India between ca. 2550 – 2530 Ma: (1) The assemblage of
various terranes of the eastern block, and (2) a tectono-magmatic event, which caused late- to posttectonic plutonism and
a thermal perturbation. It differs, however, from the pre-peak metamorphic gold mineralization at Kolar and the single-stage
mineralization at Ramagiri. Notably, greenschist facies gold mineralization occurred at Hutti 35–90 million years later than
in the western Dharwar craton.
Editorial handling: G. Beaudoin 相似文献
2.
Gold deposits at El Sid are confined to hydrothermal quartz veins which contain pyrite, arsenopyrite, sphalerite and galena. These veins occur at the contact between granite and serpentinite and extend into the serpentinite through a thick zone of graphite schist. Gold occurs in the mineralized zone either as free gold in quartz gangue or dissolved in the sulfide minerals. Ore-microscopic study revealed that Au-bearing sulfides were deposited in two successive stages with early pyrite and arsenopyrite followed by sphalerite and galena. Gold was deposited during both stages, largely intergrown with sphalerite and filling microfractures in pyrite and arsenopyrite.Spectrochemical analyses of separated pyrite, arsenopyrite, sphalerite and galena showed that these sulfides have similar average Au contents. Pyrite is relatively depleted in Ag and Te. This suggests that native gold was deposited in the early stage of mineralization. Arsenopyrite and galena show relatively high concentrations of Te. They are also respectively rich in Au and Ag. Tellurides are, thus, expected to be deposited together with arsenopyrite and galena. 相似文献
3.
The Penjom gold deposit lies on the eastern side of the Raub‐Bentong Suture line within the Central Belt of Permo‐Triassic rocks, near Kuala Lipis, Pahang, Malaysia. The geology of the deposit is dominated by a sequence of fine‐ to coarse‐grained rhyolitic to rhyodacitic tuff, tuff‐breccia and a minor rhyolitic–rhyodacitic volcanic series, associated with argillaceous marine sedimentary rocks consisting of shale with subordinate shalely limestone of Padang Tungku Formation and Pahang Volcanic Series. Fine‐ to coarse‐grained tonalite and quartz porphyry intruded this unit. The main structural features of the area are north–south‐trending left‐lateral strike‐slip faults and their subsidiaries, which generally strike north–south and dip moderately to the east (350°–360°/40°–60°). Mineralization at the Penjom gold deposit is structurally controlled and also erratic laterally and vertically. The gold mineralization can be categorized as (i) gold associated with carbonate‐rich zones hosted within dilated quartz veins carrying significant amount of sulfides; (ii) gold disseminated within stockwork of quartz–carbonate veins affiliated with tonalite; and (iii) gold often associated with arsenopyrite and pyrite in quartz–carbonate veins and stringers hosted within shear zones of brittle–ductile nature in all rock types and in brittle fractured rhyodacitic volcanic rocks. Sphalerite, chalcopyrite, tetrahedrite and pyrrhotite are the minerals accompanying the early stage of gold mineralization. These minerals also suffered from local brittle deformation. However, most of the gold mineralization took place after the deposition of these sulfides. Galena appears somewhat towards the end of gold mineralization, whereas tellurium and bismuth accompanied gold contemporaneously. The gold mineralization occurred most probably due to the metamorphogenic deformational origin concentrated mostly in the shear zone. The mineralization is strongly controlled by the wall rock (e.g. graphitic shale), the sulfide minerals and fluid–rock interaction. 相似文献
4.
Leon Bagas David L. Huston James Anderson Terrence P. Mernagh 《Mineralium Deposita》2007,42(1-2):127-144
Significant gold deposits in the western Tanami region of Western Australia include deposits in the Bald Hill and Coyote areas. The ca. 1,864 Ma Bald Hill sequence of turbiditic and mafic volcanic rocks hosts the Kookaburra and Sandpiper deposits and a number of smaller prospects. The ca. 1,835 Ma turbiditic Killi Killi Formation hosts the Coyote deposit and several nearby prospects. The Kookaburra deposit forms as a saddle reef within a syncline, and the Sandpiper deposit is localized within graphitic metasedimentary rocks along a limb of an anticline. Gold in these deposits is hosted by anastomosing quartz–(–pyrite–arsenopyrite) veins within quartz–sericite schist with disseminated arsenopyrite, pyrite, and marcasite (after pyrrhotite). Based on relative timing relationships with structural elements, the auriferous veins are interpreted to have been emplaced before or during the ca. 1,835–1,825 Ma Tanami Orogeny (regional D1). Gold deposition is thought to have been caused by pressure drops associated with saddle reef formation (Kookaburra) and chemical reactions with graphitic rocks (Sandpiper). The Coyote deposit, the largest in the western Tanami region, consists of a number of ore lenses localized along the limbs of the Coyote Anticline, which formed during the Tanami Orogeny. The largest lenses are associated with the Gonzalez Fault, which is located along the steeply dipping southern limb of this fold. Gold was introduced at ca. 1,790 Ma into dilatant zones that formed in local perturbations along this fault during later reactivation (regional D5) towards the end of a period of granite emplacement. Gold is associated with quartz–chlorite–pyrite–(arsenopyrite–galena–sphalerite) veins with narrow (<?5 mm) chloritic selvages. A quartz–muscovite–biotite–K–feldspar–(tourmaline–actinolite–arsenopyrite) assemblage, which is interpreted to relate to granite emplacement, overprints the regional greenschist facies metamorphic assemblage. The mineralogical similarity between this overprinting assemblage and the vein assemblage suggests that the auriferous veins at the Coyote deposit are associated with the granite-related metamorphic–metasomatic assemblage. Gold deposition is thought to have been caused by pressure drops within dilatant zones. 相似文献
5.
6.
Geological and structural controls on gold mineralization in the Tanami District, Northern Territory
Gold mineralization in the Tanami district is hosted within moderately northwest dipping turbiditic sedimentary and basaltic
volcanic rocks of the Paleoproterozoic Mt. Charles Formation. The gold occurs within a complex sinistral wrench-fault array
and associated veins and alteration haloes. The main mineralized faults have a northerly trend and dip steeply east. Subsidiary
structures trend at 030° and 070° and dip towards the southeast. Paleostress calculations based on fault striation populations
and geometry (strike and dip) of faults indicate that at the time of the mineralizing event, σ
1 was sub-horizontal and SE–NW directed with σ
2 subvertical. Structural studies indicate that the mineralization occurred after the regional folding event and synchronous
with the emplacement of felsic dykes into the mine sequence. Gold veins in the Tanami district are interpreted to be part
of an outer thermal aureole gold system that formed during the emplacement of granitoids in the nearby ∼1,815 to ∼1,799 Ma
Frankenia and/or Coomarie domes. Economic gold mineralization occurred late in the paragenetic history of the district. Gold
is hosted by quartz-carbonate veins within shear zones, and also in the surrounding sericite- quartz- pyrite ± carbonate-altered
wallrocks. Gold-mineralized veins precipitated at depths of 3 to 6 km from high temperature (∼300°C), low salinity (∼5 wt%
NaCl equivalent) fluids with low CO2 contents. Barren quartz, dolomite and calcite veins that occur in pre- and post-mineralization thrust faults formed from
high salinity (∼20 wt% NaCl equivalent), low temperature (∼120–150°C) basinal brines. Pyrite in the gold mineralized veins
and alteration halos has lower δ
34S values (6.8 to 12.5‰) than local diagenetic pyrite (17.8 to 19.2‰) or pyrite in pre-mineralization thrust faults (31.7 to
37.1‰). The mineralizing fluids are inferred to have contained a well-homogenized mixture of magmatic and sedimentary-derived
sulfur.
Editorial handling: D. Huston 相似文献
7.
The Bahcecik prospect is located in the eastern Pontide tectonic province of the eastern Black Sea region of Turkey. It is one of the first low sulfidation epithermal systems to be described from this area of Turkey. Gold mineralization occurred within Late Cretaceous to early Tertiary volcanic rocks and is localized along east-trending normal faults and lithologic contacts. An early quartz–sericite alteration event was focused along the major fault in the area and resulted in precipitation of arsenian (?) pyrite with anomalous gold. A later, more spatially extensive, advanced argillic alteration event overprinted the quartz–sericite event. Native gold was precipitated during this event as disseminations and fracture fillings in quartz. Gold mineralization is restricted to the high-temperature portion of the alteration zone characterized by quartz veins with diaspore–pyrophyllite selvages. The prospect area was subjected to Tertiary to Holocene supergene alteration. 相似文献
8.
Relationships between gold concentration and structure in quartz veins from the Hodgkinson Province, northeastern Australia 总被引：1，自引：0，他引：1
The Hodgkinson Province is a tract of␣multiply deformed Silurian-Devonian rocks in north␣Queensland, Australia. Gold-bearing
quartz veins from the West Normanby Goldfield in the northern Hodgkinson Province were emplaced during the Permian D4 event, broadly coeval with regional granite emplacement. Taylors Fault, a major structure that formed during D2, hosts the veins which infill dilatational jogs opened during sinistral-normal reactivation of the fault in D4. Veins contain graphitic laminations that formed when fault planes segmented wallrocks adjacent to the veins, producing tabular
clasts that were tectonically sliced into the reefs. Laminations are the result of progressive shear strain, associated with
continued movement on the faults, which caused strain-enhanced dissolution of silicate minerals and residual graphite enrichment
in the clasts. This process produced graphite-coated shear planes that delimit zones of grain size reduction in the veins.
Laminations commonly contain stylolites, which nucleated on pronounced sinuosities of the shear planes due to progressive
shortening during D4. Gold particles have preferentially nucleated in zones of relatively coarser-grained quartz adjacent to the shear planes,
where shortening strain caused microfracturing and allowed fluid access. Gold may have been introduced with the quartz, but
was redistributed within the reefs and localized along the laminations by the effects of synchronous, progressive deformation.
Regionally, gold deposits show close spatial relationships with granite plutons of the Permian Whypalla Supersuite. Relationships
in the West Normanby Gold Field support a regional model of reef emplacement and gold mineralization during the Permian D4 event.
Received: 24 August 1997 / Accepted: 14 October 1997 相似文献
9.
M. A. Hough F. P. Bierlein L. Ailleres S. McKnight 《Australian Journal of Earth Sciences》2013,60(7):969-992
The Walhalla-Woods Point Goldfield in southeast Australia is characterised by large gold deposits associated with a Late Devonian dyke swarm. The setting of this goldfield is unique because unlike the major gold deposits in Victoria, it occurs close to the eastern margin of the Western Lachlan Orogen, and highlights the disparities between the evolving phases of orogenic gold mineralisation in the Western Lachlan Orogen, and the contrasts between sediment hosted, dyke-associated and dyke-hosted gold mineralisation. This study integrates existing and new data from renewed mapping of the geology and geochemistry of three gold deposits near the township of Walhalla, in the historically important yet under-explored and under-researched Walhalla-Woods Point Goldfield. The ten highest yielding deposits within the goldfield are either hosted within, or adjacent to, intrusions of the Woods Point Dyke Swarm. This is due to the greater chemical reactivity of the calc-alkaline dykes, and the greater rheological contrast between the dykes and surrounding low-grade metasedimentary units, which allowed for the formation of dyke-hosted quartz breccia veins that are consistently favourable sites for gold mineralisation in the Walhalla Goldfield. This is in contrast to historical production, which concentrated on visible gold within the shear zone-hosted laminated quartz veins. Gold and As assay results have highlighted the increased levels of invisible gold disseminated along dyke margins in proximity to shear zones and quartz reefs. The high-yielding gold deposits hosted wholly by the dyke intrusions of the Woods Point Dyke Swarm are orogenic gold deposits, as they are not associated with elevated levels of Bi, W, As, Mb, Te and Sb, typical of intrusion-related gold deposits. 相似文献
10.
甘肃阳山金矿是迄今为止中国发现的最大金矿。已发现的6个矿段均赋存于泥盆系中,矿石中金属矿物主要为黄铁矿和毒砂。黄铁矿有3种类型:微细粒浸染状、半自形颗粒集合体、自形单晶大颗粒;主要分布在千枚岩、花岗闪长岩、石英脉里,具有多期次多类型的特点。根据黄铁矿的特征,金矿化与石英脉体中细粒浸染状的一期黄铁矿有关。黄铁矿为重要的载金矿物之一,自然金(Au)主要以微细粒的形式赋存于黄铁矿晶体的裂隙内以及晶体与晶体的空隙间。黄铁矿赋存状态和分布特征的研究,对矿区进一步找矿具有指导意义。 相似文献
11.
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
12.
Gold mineralization of the Hutti mine, southern India, is situated in closely spaced laminated quartz veins and associated alteration haloes along steeply dipping shear zones within a sequence of rather uniform amphibolites. Intense shearing has resulted in large-scale mylonitization of the wall rocks. Anastomosing shear zones, with intervening lensoid bodies of unsheared amphibolites, are characteristic features of the deposit. The general pattern of symmetrical alteration comprises a distal zone of chlorite-rich rock, with a proximal biotite-rich zone adjacent to laminated quartz veins. Arsenopyrite thermometry yielded a temperature range of 350-477 °C for the biotite alteration zone, which preceded the formation of the laminated quartz veins. Mass balance calculations on the alteration zones indicate a gradual mass and volume loss during alteration. The alteration is accompanied by intense potash metasomatism and addition of sulfur, which resulted in the formation of arsenopyrite, pyrrhotite, and pyrite. Results of fluid inclusion studies suggest that low salinity (3.9-13.5 wt% NaCl equivalent) H2O-CO2 rich fluids were responsible for gold-rich laminated quartz vein formation in the Hutti deposit. These fluids constituted a later counterpart of the protracted fluid activity that first formed the biotite alteration zone. The estimated P-T values range from 1.0 to 1.7 kbar at 280-320 °C. These data, along with the alteration assemblages and the characteristic gold-sulfide association, both in the altered wall rock and laminated quartz veins, suggest that gold, transported as reduced bisulfide complexes, was deposited in response to sulfidation reactions in the wall rocks. Comparison of P-T conditions of formation of gold-quartz veins at Hutti with two other large gold deposits in the eastern Dharwar Craton, namely Kolar (1.8 kbar/280 °C) and western Ramagiri (1.45-1.7 kbar/240-270 °C), indicates broadly similar lode-gold forming conditions in the Dharwar Craton. 相似文献
13.
The Sukari Gold Mine,Eastern Desert—Egypt: structural setting,mineralogy and fluid inclusion study 总被引：1，自引：0，他引：1
The Sukari gold mine (18.8 Mt @ 2.14 g/t Au) is located 15 km west of the Red Sea coast in the southern central Eastern Desert of Egypt. The vein-type deposit is hosted in Late Neoproterozoic granite that intruded island-arc and ophiolite rock assemblages. The vein-forming process is related to overall late Pan-African shear and extension tectonics. At Sukari, bulk NE–SW strike-slip deformation was accommodated by a local flower structure and extensional faults with veins that formed initially at conditions of about 300 °C and 1.5–2 kbar. Gold is associated with sulfides in quartz veins and in alteration zones. Pyrite and arsenopyrite dominate the sulfide ore beside minor sphalerite, chalcopyrite and galena. Gold occurs in three distinct positions: (1) anhedral grains (GI) at the contact between As-rich zones within the arsenian pyrite; (2) randomly distributed anhedral grains (GII) and along cracks in arsenian pyrite and arsenopyrite, and (3) large gold grains (GIII) interstitial to fine-grained pyrite and arsenopyrite. Fluid inclusion studies yield minimum vein-formation temperatures and pressures between 96 and 188 °C, 210 and 1,890 bar, respectively, which is in the range of epi- to mesothermal hydrothermal ore deposits. The structural evolution of the area suggests a long-term, cyclic process of repeated veining and leaching followed by sealing, initiated by the intrusion of granodiorite. This cyclic process explains the mineralogical features and is responsible for the predicted gold reserves of the Sukari deposits. A characteristic feature of the Sukari gold mineralization is the co-precipitation of gold and arsenic in pyrite and arsenopyrite.Editorial handling: H. Frimmel 相似文献
14.
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
15.
笔者应用岩石学、构造学、矿床学、地球化学等手段和方法研究了该区金矿床的特点和形成条件,结果表明青龙河金矿的容矿岩石是一套成分以火山(碎屑)岩岩屑为主的浊积岩,其含金量高达2.87g/t,且金主要与硫化物共生,浊积岩是金的矿源层。矿区内有细脉浸染型和含金石英脉型矿床。金矿的形成受浊流作用、火山作用和后生热液作用的控制。 相似文献
16.
The Qolqoleh gold deposit is located in the northwestern part of the Sanandai‐Sirjan Zone, northwest of Iran. Gold mineralization in the Qolqoleh deposit is almost entirely confined to a series of steeply dipping ductile–brittle shear zones generated during Late Cretaceous–Tertiary continental collision between the Afro‐Arabian and the Iranian microcontinent. The host rocks are Mesozoic volcano‐sedimentary sequences consisting of felsic to mafic metavolcanics, which are metamorphosed to greenschist facies, sericite and chlorite schists. The gold orebodies were found within strong ductile deformation to late brittle deformation. Ore‐controlling structure is NE–SW‐trending oblique thrust with vergence toward south ductile–brittle shear zone. The highly strained host rocks show a combination of mylonitic and cataclastic microstructures, including crystal–plastic deformation and grain size reduction by recrystalization of quartz and mica. The gold orebodies are composed of Au‐bearing highly deformed and altered mylonitic host rocks and cross‐cutting Au‐ and sulfide‐bearing quartz veins. Approximately half of the mineralization is in the form of dissemination in the mylonite and the remainder was clearly emplaced as a result of brittle deformation in quartz–sulfide microfractures, microveins and veins. Only low volumes of gold concentration was introduced during ductile deformation, whereas, during the evident brittle deformation phase, competence contrasts allowed fracturing to focus on the quartz–sericite domain boundaries of the mylonitic foliation, thus permitting the introduction of auriferous fluid to create disseminated and cross‐cutting Au‐quartz veins. According to mineral assemblages and alteration intensity, hydrothermal alteration could be divided into three zones: silicification and sulfidation zone (major ore body); sericite and carbonate alteration zone; and sericite–chlorite alteration zone that may be taken to imply wall‐rock interaction with near neutral fluids (pH 5–6). Silicified and sulfide alteration zone is observed in the inner parts of alteration zones. High gold grades belong to silicified highly deformed mylonitic and ultramylonitic domains and silicified sulfide‐bearing microveins. Based on paragenetic relationships, three main stages of mineralization are recognized in the Qolqoleh gold deposit. Stage I encompasses deposition of large volumes of milky quartz and pyrite. Stage II includes gray and buck quartz, pyrite and minor calcite, sphalerite, subordinate chalcopyrite and gold ores. Stage III consists of comb quartz and calcite, magnetite, sphalerite, chalcopyrite, arsenopyrite, pyrrhotite and gold ores. Studies on regional geology, ore geology and ore‐forming stages have proved that the Qolqoleh deposit was formed in the compression–extension stage during the Late Cretaceous–Tertiary continental collision in a ductile–brittle shear zone, and is characterized by orogenic gold deposits. 相似文献
17.
《International Geology Review》2012,54(15):1885-1901
The Dachang gold deposit is located in the Late Triassic Songpan-Ganzi Fold Belt, NE Tibetan Plateau. Gold ore is concentrated as veins along secondary faults and fracture zones in the Bayan Har Group metaturbidites. No exposed felsic plutons are present in the vicinity of the deposit. The auriferous veins contain <15% sulphide minerals, mainly arsenopyrite, pyrite, and stibnite. Gold is commonly enclosed within arsenopyrite and pyrite. Typical alteration around the ore bodies includes silicification, sericitization, and weak carbonatization.Gold-bearing quartz samples have δ18O values of 16.9–21.2‰ (V-SMOW) from which δ18OH2O values of 6.2–9.6‰ can be calculated from the fluid inclusion temperatures (or 10.0 to 12.7‰ if we used the average arsenopyrite geothermometer temperature of 301°C). The δD values of fluid inclusions in quartz range from –90‰ to –72‰. δ34S values of gold-bearing sulphides mainly range from –5.9‰ to –2.8‰ (V-CDT). Pyrite and arsenopyrite in ores have 206Pb/204Pb ratios of 18.2888 to 18.4702, 207Pb/204Pb ratios of 15.5763 to 15.6712, and 208Pb/204Pb ratios of 38.2298 to 38.8212. These isotopic compositions indicate that the ore-forming fluids were of metamorphic origin, and the S and Pb may have been derived from the host metaturbidites of the Bayan Har Group. The Dachang Au deposit has geological and geochemical features similar to orogenic gold deposits. We propose that the ores formed when the Songpan-Ganzi Fold Belt was intensely deformed by Late Triassic folding and thrusting. Large-scale thrusting resulted in regional allochthons of different scales, followed by secondary faults or fracture zones that controlled the ore bodies. 相似文献
18.
丘岭金矿床是西秦岭地区重要的卡林型金矿之一, 金矿化赋存于上泥盆统南阳山组和下石炭统袁家沟组地层中, 容矿岩石的岩性为钙质粉砂岩、粉砂质页岩和泥质灰岩.金矿石中主要金属矿物为黄铁矿和毒砂, 非金属矿物则以石英、方解石和绢云母为主.通过对矿石矿物黄铁矿和毒砂的扫描电镜-能谱分析、电子探针分析和激光剥蚀电感耦合等离子体质谱分析, 对丘岭金矿床金的赋存形式和富集机理进行了较为详细的研究.结果表明, 丘岭金矿床中金主要以次显微不可见金的形式存在, 其次为显微可见金.次显微金包括: (1)固溶体金(Au+), 主要存在于环带状细粒黄铁矿的含砷增生边区域和毒砂中, 少量存在于环带状黄铁矿的核部不含砷区域; (2)纳米级自然金颗粒(Au0), 存在于粗晶黄铁矿中.环带状细粒黄铁矿核部的次显微金可能主要以胶体吸附的形式存在, 暗示容矿岩石在沉积成岩过程中有金的初步富集, 而环带状黄铁矿幔部和毒砂中的Au则主要来源于成矿流体, 以S和As的络合物形式搬运.显微可见金主要分布在细粒黄铁矿的晶体边缘和热液蚀变绢云母、石英及方解石中, 粒径通常小于3~5 μm, 其形成可能与成矿流体中金的局部过饱和及成矿流体对细粒黄铁矿和毒砂中次显微金的活化和再次富集有关. 相似文献
19.
The Mirge-Naqshineh gold district is situated at northwest of Iran with a NW-trending brittleductile shear zone. It is hosted by Precambrian meta-sedimentary and meta-volcanic units traversed by mineralized quartz veins. In terms of cross-cutting relationships and sulfide content three types of quartz veins are identified in the region. Among those, parallel to bedding quartz vein(type Ⅰ) is the main host for gold mineralization. Gold is found in three different forms: 1) submicrometer-size inclusions of gold in arsenian pyrite, 2) as electrum and 3) in the crystal lattice of sulfides(pyrite, galena and chalcopyrite). Six types of pyrite(Py1-Py6) were identified in this ore reserve. Py3 coexists with arsenopyrite and contains the greatest As-Au concentrations. There is a negative correlation between the As and S contents in Py2 and Py3, implying the substitution of sulfur by arsenic. Pyrites and mineralized quartz veins were formed via metamorphic-hydrothermal fluid and reflect the gold-transportation as Au(HS)_2~- under reducing and acidic conditions. The gold precipitation mainly controlled by crystallization of arsenian pyrite during fluid/rock interactions and variation of fO_2. The volcanic host rock has played an important role in gold concentration, as Py3 in this rock contains inclusion of gold particles, but gold is within the lattice of pyrite in phyllite or other units. 相似文献
20.
Three types of base metal deposits occur in the Devonian of the Central Pyrenees accompanying and post-dating the Hercynian
orogeny. Since spatial and temporal relationships between mineralization can be recognized in the Yenefrito area, they have
been incorporated into a metallogenetic model. Sedex-like ore, composed of sphalerite with minor galena, pyrite, arsenopyrite
and magnetite, is enclosed within a carbonate-siltstone succession containing volcanic sills. Crust-type mineralization is
linked to an unconformity landscape and made up by quartz and minor sphalerite, pyrite and galena. Finally, vein deposit cross-cutting
these deposit types, contains galena, sphalerite and pyrite. Sedex-like and crust-type deposits are linked to Hercynian extensional
tectonics which favoured the development of an unstable depositional environment mainly controlled by synsedimentary faults,
being sedex mineralizations developed prior to crust-type. Both mineralization types suffered diagenesis and deformation during
the Hercynian. The vein-type was generated by extensional movements related to early Alpine rifting.
Received: 18 June 1998 / Accepted: 30 June 1998 相似文献