首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 438 毫秒
1.
The Laloki and Federal Flag deposits are two of the many (over 45) polymetallic massive sulfide deposits that occur in the Astrolabe Mineral Field, Papua New Guinea. New data of the mineralogical compositions, mineral textures, and fluid inclusion studies on sphalerite from Laloki and Federal Flag deposits were investigated to clarify physiochemical conditions of the mineralization at both deposits. The two deposits are located about 2 km apart and they are stratigraphically hosted by siliceous to carbonaceous claystone and rare gray chert of Paleocene–Eocene age. Massive sulfide ore and host rock samples were collected from each deposit for mineralogical, geochemical, and fluid inclusion studies. Mineralization at the Laloki deposit consists of early‐stage massive sulfide mineralization (sphalerite‐barite, chalcopyrite, and pyrite–marcasite) and late‐stage brecciation and remobilization of early‐stage massive sulfides that was accompanied by late‐stage sphalerite mineralization. Occurrence of native gold blebs in early‐stage massive pyrite–marcasite‐chalcopyrite ore with the association of pyrrhotite‐hematite and abundant planktonic foraminifera remnants was due to reduction of hydrothermal fluids by the reaction with organic‐rich sediments and seawater mixing. Precipitation of fine‐grained gold blebs in late‐stage Fe‐rich sphalerite resulted from low temperature and higher salinity ore fluids in sulfur reducing conditions. In contrast, the massive sulfide ores from the Federal Flag deposit contain Fe‐rich sphalerite and subordinate sulfarsenides. Native gold blebs occur as inclusions in Fe‐rich sphalerite, along sphalerite grain boundaries, and in the siliceous‐hematitic matrix. Such occurrences of native gold suggest that gold was initially precipitated from high‐temperature, moderate to highly reduced, low‐sulfur ore fluids. Concentrations of Au and Ag from both Laloki and Federal Flag deposits were within the range (<10 ppm Au and <100 ppm Ag) of massive sulfides at a mid‐ocean ridge setting rather than typical arc‐type massive sulfides. The complex relationship between FeS contents in sphalerite and gold grades of both deposits is probably due to the initial deposition of gold on the seafloor that may have been controlled by factors such as Au complexes, pH, and fO2 in combination with temperature and sulfur fugacity.  相似文献   

2.
Mineralogic studies of major ore minerals and fluid inclusion analysis in gangue quartz were carried out for the for the two largest veins, the Aginskoe and Surprise, in the Late Miocene Aginskoe Au–Ag–Te deposit in central Kamchatka, Russia. The veins consist of quartz–adularia–calcite gangue, which are hosted by Late Miocene andesitic and basaltic rocks of the Alnei Formation. The major ore minerals in these veins are native gold, altaite, petzite, hessite, calaverite, sphalerite, and chalcopyrite. Minor and trace minerals are pyrite, galena, and acanthine. Primary gold occurs as free grains, inclusions in sulfides, and constituent in tellurides. Secondary gold is present in form of native mustard gold that usually occur in Fe‐hydroxides and accumulates on the decomposed primary Au‐bearing tellurides such as calaverite, krennerite, and sylvanite. K–Ar dating on vein adularia yielded age of mineralization 7.1–6.9 Ma. Mineralization of the deposit is divided into barren massive quartz (stage I), Au–Ag–Te mineralization occurring in quartz‐adularia‐clays banded ore (Stage II), intensive brecciation (Stage III), post‐ore coarse amethyst (Stage IV), carbonate (Stage V), and supergene stages (Stage VI). In the supergene stage various secondary minerals, including rare bilibinskite, bogdanovite, bessmertnovite metallic alloys, secondary gold, and various oxides, formed under intensely oxidized conditions. Despite heavy oxidation of the ores in the deposit, Te and S fugacities are estimated as Stage II tellurides precipitated at the log f Te2 values ?9 and at log fS2 ?13 based on the chemical compositions of hypogene tellurides and sphalerite. Homogenization temperature of fluid inclusions in quartz broadly ranges from 200 to 300°C. Ore texture, fluid inclusions, gangue, and vein mineral assemblages indicate that the Aginskoe deposit is a low‐sulfidation (quartz–adularia–sericite) vein system.  相似文献   

3.
Abstract: Mineral paragenesis of the alteration, ore and gangue minerals of the Lepanto epithermal copper‐gold deposit and the Victoria gold deposit, Mankayan Mineral District, Northern Luzon, Philippines, is discussed. The principal ore minerals of the Lepanto copper‐gold deposit are enargite and luzonite, with significant presence of tennantite‐tetrahedrite, chalcopyrite, sphalerite, galena, native gold/electrum and gold‐silver tellurides. Pervasive alteration zonations are commonly observed from silicification outward to advanced argillic then to propylitic zone. The ore mineralogy of the Lepanto copper‐gold deposit suggests high fS2 in the early stages of mineralization corresponding to the deposition of the enargite‐luzonite‐pyrite assemblage. Subsequent decrease in the fS2 formed the chalcopyrite‐tennantite‐pyrite assemblage. An increase in the fS2 of the fluids with the formation of the covellite‐digenite‐telluride assemblage caused the deposition of native gold/electrum and gold‐silver tellurides. The principal ore minerals of the Victoria gold deposit are sphalerite, galena, chalcopyrite, tetrahedrite and native gold/electrum. The alteration halos are relatively narrow and in an outward sequence from the ore, silica alteration grades to illitic‐argillic alteration, which in turn grades to propylitic alteration. The Victoria gold mineralization has undergone early stages of silica supersaturation leading to quartz deposition. Vigorous boiling increased the pH of the fluids that led to the deposition of sulfides and carbonates. The consequent decrease in H2S precipitated the gold. Gypsum and anhydrite mainly occur as overprints that cut the carbonate‐silica stages. The crosscutting and overprinting relationships of the Victoria quartz‐gold‐base metal veins on the Lepanto copper‐gold veins manifest the late introduction of near neutral pH hydrothermal fluids.  相似文献   

4.
毕诗健  李占轲  唐克非  高凯 《地球科学》2016,41(7):1121-1140
位于华北克拉通南缘的小秦岭地区是我国仅次于胶东的大型金矿床集中区,但金矿床的成矿物质来源及成因问题一直存在较大争议.以华北南缘小秦岭矿集区东桐峪金矿床中的黄铁矿作为研究对象,在黄铁矿显微结构研究的基础上利用LA-ICP-MS对黄铁矿的微量元素进行原位分析,为进一步认识东桐峪金矿床及区内其他同类型矿床的成因提供新的资料和制约.东桐峪金矿床的黄铁矿从早到晚依次划分为3个世代(PyⅠ、PyⅡ和PyⅢ).PyⅠ主要形成于粗粒黄铁矿-石英阶段,颗粒粗大且自形程度高,呈星点状或斑点状赋存于乳白色石英脉中.PyⅡ主要形成于石英-中细粒黄铁矿阶段,呈半自形-他形结构且裂隙发育,常被晚期石英、多金属硫化物、自然金等矿物充填.PyⅢ主要形成于多金属硫化物阶段,常呈他形粒状结构与黄铜矿、方铅矿及闪锌矿等硫化物密切共生.LA-ICP-MS分析结果显示,PyⅠ中As平均含量为16.63×10-6,Au、Ag和Te含量较低且常位于检测限以下;相较而言,PyⅡ中As含量稍低,而Au、Ag和Te含量略高(其中Au含量为0.10×10-6~0.59×10-6);PyⅢ中Au、Ag和Te含量差异较大且显著升高,其中Au、Te含量最高可达35.58×10-6和79.79×10-6,而As含量较低且大部分数值低于检测限;不同世代黄铁矿的Co/Ni比值基本上都大于1,且PyⅢ的Co、Ni含量和Co/Ni比值明显低于PyⅡ和PyⅠ.以上结果表明,东桐峪金矿床的载金矿物黄铁矿中As的含量很低,金的富集与As无关;不同世代的黄铁矿中Au、Ag和Te之间存在显著且稳定的线性正相关关系,暗示金矿化与Te关系密切.另外,第3世代黄铁矿(PyⅢ)中Au、Ag及Te存在显著富集,指示Te(而不是As)在金和银的迁移、搬运、富集、沉淀等过程中具有重要作用.华北克拉通南缘小秦岭地区晚中生代大规模的金成矿作用及金矿床中普遍存在Te-Au-Ag矿物,且黄铁矿中As含量低、Te含量高等特征,暗示该区金矿床的成矿物质/成矿流体可能来自深部岩浆的脱挥发分或地幔脱气作用,而与区域变质作用的关系不大.   相似文献   

5.
The Bianbianshan deposit, the unique gold-polymetal (Au-Ag-Cu-Pb-Zn) veined deposit of the polymetal metallogenic belt of the southern segment of Da Hinggan Mountains mineral province, is located at the southern part of the Hercynian fold belt of the south segment of Da Hinggan Mountains mineral province, NE China. Ores at the Bianbianshan deposit occur within Cretaceous andesite and rhyolite in the form of gold-bearing quartz veins and veinlet groups containing native gold, electrum, pyrite, chalcopyrite, galena and sphalerite. The deposit is hosted by structurally controlled faults associated with intense hydrothermal alteration. The typical alteration assemblage is sericite + chlorite + calcite + quartz, with an inner pyrite - sericite - quartz zone and an outer seicite - chlorite - calcite - epidote zone between orebodies and wall rocks. δ34 S values of 17 sulfides from ores changing from –1.67 to +0.49‰ with average of –0.49‰, are similar to δ34 S values of magmatic or igneous sulfide sulfur. 206Pb/204Pb, 207Pb/204Pb and 208Pb/ 204Pb data of sulfide from ores range within 17.66–17.75, 15.50–15.60, and 37.64–38.00, respectively. These sulfur and lead isotope compositions imply that ore-forming materials might mainly originate from deep sources. H and O isotope study of quartz from ore-bearing veins indicate a mixed source of deep-seated magmatic water and shallower meteoric water. The ore formations resulted from a combination of hydrothermal fluid mixing and a structural setting favoring gold-polymetal deposition. Fluid mixing was possibly the key factor resulting in Au-Ag-Cu-Pb-Zn deposition in the deposit. The metallogenesis of the Bianbianshan deposit may have a relationship with the Cretaceous volcanic-subvolcanic magmatic activity, and formed during the late stage of the crust thinning of North China.  相似文献   

6.
Orogenic Gold Mineralization in the Qolqoleh Deposit, Northwestern Iran   总被引：1，自引：1，他引：1  
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   

7.
The Mesozoic Yangzhaiyu lode gold deposit is situated in the southern edge of the North China craton. Gold mineralization is hosted in Archean amphibolite facies metamorphic rocks, and consists mainly of auriferous quartz veins. Pyrite is the predominant sulfide mineral, with minor amounts of chalcopyrite, sphalerite, and galena. Based on morphology and paragenesis, there are three generations of pyrite, termed as first generation (G1), second generation (G2), and third generation (G3). They have distinct contents, occurrences, and distribution patterns of gold. The coarse-grained, euhedral G1 pyrite contains negligible to low levels of gold, whereas both invisible and visible gold are present in the fine- to medium-grained G2 pyrite that is characterized by abundance of microfractures and porosities, forming a foam-like texture. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) depth profiles indicate that invisible gold occurs either as solid solution or as nanoparticles of gold-bearing tellurides in the G2 pyrite. Visible gold is widespread and present as irregular grains and stringers of native gold mostly along grain boundaries or filling microfractures of pyrite, likely resulting from remobilization of invisible gold once locked in the G2 pyrite. The G3 pyrite, invariably intergrown with chalcopyrite, sphalerite, and galena, contains the highest levels of invisible gold. There is a positive correlation between Au, Ag, and Te, indicating that gold occurs as submicroscopic Au-bearing telluride inclusions in the host minerals. Whenever gold, either invisible or visible, is present, As is always below or only marginally higher than the detection limit of LA-ICP-MS. This indicates that As played an insignificant role in gold mineralization. Tellurides are widespread in the auriferous quartz veins, consisting mainly of petzite, calaverite, hessite, altaite, and tellurobismuthite. Native gold commonly occurs as intergrowths with tellurides. Textural evidence indicates a precipitation sequence, in a temporal order, of calcaverite, petzite, altaite, tellurobismuthite, and hessite. Little amount of sulfide phases has been found in association with the tellurides, indicating that tellurides were deposited under low S fugacity (fS 2 ) and/or high Te fugacity (fTe 2 ) conditions. The textural relationships, when combined with fluid inclusion microthermometric data of auriferous quartz veins and tellurides thermodynamic data, permit estimation for logfTe 2 during telluride formation, which are −6.8 to −10.8 at 300°C and −9.6 to −17.6 at 250°C. Available geochronological and geochemical data suggest that Te was most likely derived from the late Mesozoic magmatic rocks widespread in the Xiaoqinling district and other parts of the southern North China craton, which were emplaced broadly contemporaneous with gold mineralization at Yangzhaiyu. This study highlights the role of Te and tellurides as important gold scavengers in As-deficient ore fluids.  相似文献   

8.
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   

9.
Ore mineralization and wall rock alteration of Crater Mountain gold deposit, Papua New Guinea, were investigated using ore and host rock samples from drill holes for ore and alteration mineralogical study. The host rocks of the deposit are quartz‐feldspar porphyry, feldspar‐hornblende porphyry, andesitic volcanics and pyroclastics, and basaltic‐andesitic tuff. The main ore minerals are pyrite, sphalerite, galena, chalcopyrite and moderate amounts of tetrahedrite, tennantite, pyrrhotite, bornite and enargite. Small amounts of enargite, tetradymite, altaite, heyrovskyite, bismuthinite, bornite, idaite, cubanite, native gold, CuPbS2, an unidentified Bi‐Te‐S mineral and argentopyrite occur as inclusions mainly in pyrite veins and grains. Native gold occurs significantly in the As‐rich pyrite veins in volcanic units, and coexists with Bi‐Te‐S mineral species and rarely with chalcopyrite and cubanite relics. Four mineralization stages were recognized based on the observations of ore textures. Stage I is characterized by quartz‐sericite‐calcite alteration with trace pyrite and chalcopyrite in the monomict diatreme breccias; Stage II is defined by the crystallization of pyrite and by weak quartz‐chlorite‐sericite‐calcite alteration; Stage III is a major ore formation episode where sulfides deposited as disseminated grains and veins that host native gold, and is divided into three sub‐stages; Stage IV is characterized by predominant carbonitization. Gold mineralization occurred in the sub‐stages 2 and 3 in Stage III. The fS2 is considered to have decreased from ～10?2 to 10?14 atm with decreasing temperature of fluid.  相似文献   

10.
The Luanling gold telluride deposit in the Xiong'ershan region is located in the southern margin of the North China Craton. The deposit formed in four stages, that is, an early pyrite‐quartz stage (I), a pyrite‐molybdenite stage (II), a sulfide‐telluride‐gold stage (III), and a late carbonate stage (IV). Six species of telluride in stage (III) are recognized, including hessite, altaite, petzite, unidentified Au‐Ag‐Te mineral, empressite, and unidentified Ag‐Te‐S mineral. Gold occurs mostly as native gold and electrum along the microfractures of sulfides or the contact between sulfide and telluride. The mineralization temperature of stage I and stage III ranges from 296 to 377°C and 241 to 324°C, respectively. Tellurides in stage III precipitate at the log?S2 from ?14.3 to ?7.3 and log?Te2 from ?17.4 to ?9.4. The ores were formed in an oxidizing environment. The Re‐Os model ages of molybdenite are 162–164 Ma, which indicate that the main ore formation stage was in the Late Jurassic. The Re contents of five molybdenite samples from the Luanling deposit have a range of 36.32–81.95 ppm, except for one large value of 220 ppm, which indicates that the ore‐forming materials are mainly derived from a crustal‐dominated source. The δ34S values of sulfides range from ?17.6 to ?6.2‰, whereas those of sulfates are from 6.8 to 11.5‰. The δ34S∑S value of the ore‐forming system is 0.0–3.7‰, indicating that the sulfur of the Luanling deposit derived from a deep igneous source. Mineral association and isotope data of the Luanling deposit, together with its geodynamic setting, imply that this deposit belongs to a part of the metallogenic system of the Nannihu‐Sandaozhuang, Shangfangou porphyry molybdenum deposits, and the Late Jurassic granitic intrusions.  相似文献   

11.
Karavansalija ore zone is situated in the Serbian part of the Serbo‐Macedonian magmatic and metallogenic belt. The Cu–Au mineralization is hosted mainly by garnet–pyroxene–epidote skarns and shifts to lesser presence towards the nearby quartz–epidotized rocks and the overlying volcanic tuffs. Within the epidosites the sulfide mineralogy is represented by disseminated cobalt‐nickel sulfides from the gersdorfite‐krutovite mineral series and cobaltite, and pyrite–marcasite–chalcopyrite–base metal aggregates. The skarn sulfide mineralization is characterized by chalcopyrite, pyrite, pyrrhotite, bismuth‐phases (bismuthinite and cosalite), arsenopyrite, gersdorffite, and sphalerite. The sulfides can be observed in several types of massive aggregates, depending on the predominant sulfide phases: pyrrhotite‐chalcopyrite aggregates with lesser amount of arsenopyrite and traces of sphalerite, arsenopyrite–bismuthinite–cosalite aggregates with subordinate sphalerite and sphalerite veins with bismuthinite, pyrite and arsenopyrite. In the overlying volcanoclastics, the studied sulfide mineralization is represented mainly by arsenopyrite aggregates with subordinate amounts of pyrite and chalcopyrite. Gold is present rarely as visible aggregate of native gold and also as invisible element included in arsenopyrite. The fluid inclusion microthermometry data suggest homogenization temperature in the range of roughly 150–400°C. Salinities vary in the ranges of 0.5–8.5 wt% NaCl eq for two‐phase low density fluid inclusions and 15–41 wt% NaCl eq for two‐phase high‐salinity and three‐phase high‐salinity fluid inclusions. The broad range of salinity values and the different types of fluid inclusions co‐existing in the same crystals suggest that at least two fluids with different salinities contributed to the formation of the Cu–Au mineralization. Geothermometry, based on EPMA data of arsenopyrite co‐existing with pyrite and pyrrhotite, suggests a temperature range of 240–360°C for the formation of the arsenopyrite, which overlaps well with the data for the formation temperature obtained through fluid inclusion microthermometry. The sulfur isotope data on arsenopyrite, chalcopyrite, pyrite and marcasite from the different sulfide assemblages (ranging from 0.4‰ to +3.9‰ δ34SCDT with average of 2.29 δ34SCDT and standard deviation of 1.34 δ34SCDT) indicates a magmatic source of sulfur for all of the investigated phases. The narrow range of the data points to a common source for all of the investigated sulfides, regardless of the host rock and the paragenesis. The sulfur isotope data shows good overlap with that from nearby base‐metal deposits; therefore the Cu–Au mineralization and the emblematic base‐metal sulfide mineralization from this metallogenic belt likely share same fluid source.  相似文献   

12.
The vein system in the Arinem area is a gold‐silver‐base metal deposit of Late Miocene (8.8–9.4 Ma) age located in the southwestern part of Java Island, Indonesia. The mineralization in the area is represented by the Arinem vein with a total length of about 5900 m, with a vertical extent up to 575 m, with other associated veins such as Bantarhuni and Halimun. The Arinem vein is hosted by andesitic tuff, breccia, and lava of the Oligocene–Middle Miocene Jampang Formation (23–11.6 Ma) and overlain unconformably by Pliocene–Pleistocene volcanic rocks composed of andesitic‐basaltic tuff, tuff breccia and lavas. The inferred reserve is approximately 2 million tons at 5.7 g t?1 gold and 41.5 g t?1 silver at a cut‐off of 4 g t?1 Au, which equates to approximately 12.5t of Au and 91.4t of Ag. The ore mineral assemblage of the Arinem vein consists of sphalerite, galena, chalcopyrite, pyrite, marcasite, and arsenopyrite with small amounts of pyrrhotite, argentite, electrum, bornite, hessite, tetradymite, altaite, petzite, stutzite, hematite, enargite, tennantite, chalcocite, and covellite. These ore minerals occur in quartz with colloform, crustiform, comb, vuggy, massive, brecciated, bladed and calcedonic textures and sulfide veins. A pervasive quartz–illite–pyrite alteration zone encloses the quartz and sulfide veins and is associated with veinlets of quartz–calcite–pyrite. This alteration zone is enveloped by smectite–illite–kaolinite–quartz–pyrite alteration, which grades into a chlorite–smectite–kaolinite–calcite–pyrite zone. Early stage mineralization (stage I) of vuggy–massive–banded crystalline quartz‐sulfide was followed by middle stage (stage II) of banded–brecciated–massive sulfide‐quartz and then by last stage (stage III) of massive‐crystalline barren quartz. The temperature of the mineralization, estimated from fluid inclusion microthermometry in quartz ranges from 157 to 325°C, whereas the temperatures indicated by fluid inclusions from sphalerite and calcite range from 153 to 218 and 140 to 217°C, respectively. The mineralizing fluid is dilute, with a salinity <4.3 wt% NaCl equiv. The ore‐mineral assemblage and paragenesis of the Arinem vein is characteristically of a low sulfidation epithermal system with indication of high sulfidation overprinted at stage II. Boiling is probably the main control for the gold solubility and precipitation of gold occurred during cooling in stage I mineralization.  相似文献   

13.
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   

14.
The Bilimoia deposit (2.23 Mt, 24 g/t Au), located in the eastern Central Mobile Belt of mainland Papua New Guinea, is composed of fault‐hosted, NW–NNW‐trending Irumafimpa–Kora and Judd–Upper Kora Au‐quartz veins hosted by Middle–Late Triassic basement that was metamorphosed to medium‐grade greenschist facies between Middle–Late Triassic and Early–Middle Jurassic. Mineralizing fluids were introduced during crustal thickening, rapid uplift, change of plate motions from oblique to orthogonal compression, active faulting and S3 and S4 events in an S1–S4 deformation sequence. The Bilimoia deposit is spatially and temporally related to I‐type, early intermediate to felsic and late mafic intrusions emplaced in Late Miocene (9–7 Ma). Hydrothermal alteration and associated mineralization is divided into 10 main paragenetic stages: (1) chlorite–epidote‐selvaged quartz–calcite–specularite vein; (2) local quartz–illite–pyrite alteration; (3) quartz–sericite–mariposite–fuchsite–pyrite wall‐rock alteration that delimits the bounding shears; (4) finely banded, colloform‐, crustiform‐ and cockade‐textured and drusy quartz ± early wolframite ± late adularia; (5) hematite; (6) pyrite; (7) quartz ± amethyst‐base metal sulfides; (8) quartz–chalcopyrite–bornite–Sn and Cu sulfides–Au tellurides and Te ± Bi ± Ag ± Cu ± Pb phases; (9) Fe ± Mn carbonates; and (10) supergene overprint. Fluid inclusions in stage 4 are characterized by low salinity (0.9–5.4 wt% NaCl equivalent), aqueous–carbonic fluids with total homogenization temperatures ranging from 210 to 330°C. Some of the inclusions that homogenized between 285 and 330°C host coexisting liquid‐ and vapor‐rich (including carbonic) phases, suggesting phase separation. Fluid inclusions in quartz intergrown with wolframite have low salinity (0.9–1.2 wt% NaCl equivalent), aqueous–carbonic fluids at 240–260°C, defining the latter’s depositional conditions. The ore fluids were derived from oxidized magmatic source initially contaminated by reduced basement rocks. Wall‐rock alteration and involvement of circulating meteoric waters were dominant during the first three stages and early part of stage 4. Stage 5 hematite was deposited as a result of stage 4 phase separation or entrainment of oxygenated groundwater. Gold is associated with Te‐ and Bi‐bearing minerals and mostly precipitated as gold‐tellurides during stage 8. Gold deposition occurred below 350°C due to a change in the sulfidation and oxidation state of the fluids, depressurization and decreasing temperature and activities of sulfur and tellurium. Bisulfides are considered to be the main Au‐transporting complexes. The Bilimoia deposit has affinities that are similar to many gold systems termed epizonal orogenic and intrusion‐related. The current data allow us to classify the Bilimoia deposit as a fault‐controlled, metamorphic‐hosted, intrusion‐related mesothermal to low sulfidation epithermal quartz–Au–Te–Bi vein system.  相似文献   

15.
<正>The Chang'an gold ore deposit in western Yunnan is located at the southern segment of the Ailaoshan metallogenic belt.The ore bodies are preserved in fractured Ordovician sedimentary clastic rocks.The gold-bearing minerals occur dominantly in sulfide-quartz veins.Fluid inclusion analysis shows that the Chang'an gold ore deposit is characterized by epithermal gold mineralization at temperatures between 200℃and 280℃at a shallow crustal level.The mineralizing fluids have intermediate to low salinity(6%-18%) and low densities(0.72-1.27 g/cm~3).The ore minerals haveδ~(34)S in a range from -13‰to 3.57‰,concentrated from -2.06‰to 3.57‰with an average of 1.55‰.The ~(206)Pb/~(204)Pb,~(207)Pb/~(204)Pb and ~(208)Pb/~(204)Pb values are 18.9977-19.5748,15.7093-15.784,39.3814-40.2004 respectively.These isotope data suggest that the ore-forming elements were mainly derived from mixed crustal and mantle sources.The Chang'an gold ore deposit and Tongchang Cu-Mo deposit are closely related to each other in their spatial distribution and age of formation.They have similar sources of mineralizing elements and identical ore-forming metal elements,and show a close relationship in physical and chemical conditions of mineralization.The two deposits constitute an epithermal-porphyry -skarn type Cu-Mo-Au mineralization system in the Tongchang-Chang'an area,which is related to the Cenozoic high-K alkaline magmatism.  相似文献   

16.
The Dongping gold deposit is located near the center of the northern margin of the North China Craton. It is hosted in the Shuiquangou syenite and characterized by large amounts of tellurides. Numerous studies have addressed this deposit; the mineral paragenesis and ore‐forming processes, however, are still poorly studied. In this contribution, a new mineral paragenesis has been evaluated to further understand ore formation, including sulfides (pyrite, chalcopyrite, galena, sphalerite, molybdenite, and bornite), tellurides (altaite, calaverite, hessite, muthmannite, petzite, rucklidgeite, sylvanite, tellurobismuthite, tetradymite, and volynskite), and native elements (tellurium and gold). Molybdenite, muthmannite, rucklidgeite, and volynskite are reported for the first time in this deposit. We consider the Dongping gold deposit mainly formed in the Devonian, and the ore‐forming processes and the physicochemical conditions for ore formation can be reconstructed based on our newly identified ore paragenesis, that is, iron oxides → (CO2 effervescence) → sulfides → (fTe2/fS2 ratio increase) → Pb‐Bi‐tellurides → (condensation of H2Te vapor) → Au‐Ag‐tellurides → (mixing with oxidizing water) → carbonate and microporous gold → secondary minerals → secondary minerals. The logfO2 values increase from the early to late stages, while the fH2S and logfS2 values increase initially and then decrease. CO2 effervescence is the main mechanism of sulfides precipitation; this sulfidation and condensation of H2Te vapor lead to deposition of tellurides. The development of microporous gold indicates that the deposit might experience overprint after mineralization. The Dongping gold deposit has a close genetic relationship with the Shuiquangou syenite, and tellurium likely originated from Shuiquangou alkaline magmatic degassing.  相似文献   

17.
Gold‐mineralized quartz veins at the Trenggalek district of the Southern Mountains Range in East Java, Indonesia, are hosted by Oligo‐Miocene volcaniclastic and volcanic rocks, and are distributed close to andesitic plugs in the northern prospects (Dalangturu, Suruh, Jati, Gregah, Jombok, Salak, and Kojan) and the southern prospects (Sentul and Buluroto). The plugs are subalkaline tholeiitic basaltic‐andesite to calc‐alkaline andesite in composition. 40Ar–39Ar dating of a quartz‐adularia vein at the Dalangturu prospect yielded an age of 16.29 ± 0.56 Ma (2σ), and a crystal tuff of a limestone‐pyroclastic rock sequence at the southwest of the Dalangturu prospect was determined as 15.6 ± 0.5 Ma (2σ). Statistic overlap of ages suggests that the gold mineralization in the northern prospects took place in a shallow marine to subaerial transitional environment. Hydrothermal alteration of the host rocks is characterized by the replacement of quartz, illite and adularia. Quartz veins in surface outcrops are up to 50 cm wide in the northern prospects and up to 3 m wide in the southern prospects, showing a banded or brecciated texture, and are composed of quartz, adularia, carbonates with pyrite, electrum, sphalerite, galena, and polybasite. Gold contents of quartz veins are positively correlated with Ag, Zn, Pb, and Cu contents in both the northern and southern prospects. The quartz veins at the Jati, Gregah, and Sentul prospects have relatively lower gold‐silver ratios (Ag/Au = 23.2) compared to those at the Kojan, Dalangturu, Salak, and Suruh prospects (Ag/Au = 66.8). The quartz veins at the Dalangturu prospect are relatively rich in base metal sulfides. Ag/(Au+Ag) ratios of electrum in the Dalangturu prospect range from 45.2 to 65.0 at%, and FeS contents of sphalerite range from 1.2 to 6.4 mol%. Fluid inclusion microthermometry indicates ore‐forming temperatures of 190–200°C and 220–230°C at the Sentul and Kojan prospects, respectively. Widely variable vapor/liquid ratio of fluid inclusions indicates that fluid boiling took place within the hydrothermal system at the Sentul prospect. Salinities of ore‐fluids range from 0 to 0.7 wt% (av. 0.4 wt% NaCl equiv.) and from 0.5 to 1.4 wt% (av. 0.9 wt%) for the Sentul and Kojan prospects, respectively. The boiling of hydrothermal fluid was one of the gold deposition mechanisms in the Sentul prospect.  相似文献   

18.
The Sawayaerdun gold deposit, located in Wuqia County, Southwest Tianshan, China, occurs in Upper Silurian and Lower Devonian low‐grade metamorphic carbonaceous turbidites. The orebodies are controlled by a series of NE‐NNE‐trending, brittle–ductile shear zones. Twenty‐four gold mineralized zones have been recognized in the Sawayaerdun ore deposit. Among these, the up to 4‐km‐long and 200‐m wide No. IV mineralized zone is economically the most important. The average gold grade is 1–6 g/t. Gold reserves of the Sawayaerdun deposit have been identified at approximately 37 tonnes and an inferred resource of 123 tonnes. Hydrothermal alteration is characterized by silicification, pyritization, arsenopyritization, sericitization, carbonatization and chloritization. On the basis of field evidence and petrographic analysis, five stages of vein emplacement and hydrothermal mineralization can be distinguished: stage 1, early quartz stage, characterized by the occurrence of quartz veins; stage 2, arsenopyrite–pyrite–quartz stage, characterized by the formation of auriferous quartz veinlets and stockworks; stage 3, polymetallic sulfide quartz stage, characterized by the presence of auriferous polymetallic sulfide quartz veinlets and stockworks; stage 4, antimony–quartz stage, characterized by the formation of stibnite–jamesonite quartz veins; and stage 5, quartz–carbonate vein stage. Stages 2 and 3 represent the main gold mineralization, with stage 4 representing a major antimony mineralization episode in the Sawayaerdun deposit. Two types of fluid inclusion, namely H2O–NaCl and H2O–CO2–NaCl types, have been recognized in quartz and calcite. Aqueous inclusions show a wide range of homogenization temperatures from 125 to 340°C, and can be correlated with the mineralization stage during which the inclusions formed. Similarly, salinities and densities of these fluids range for each stage of mineralization from 2.57 to 22 equivalent wt% NaCl and 0.76 to 1.05 g/cm3, respectively. The ore‐forming fluids thus are representative of a medium‐ to low‐temperature, low‐ to medium‐salinity H2O–NaCl–CO2–CH4–N2 system. The δ34SCDT values of sulfides associated with mineralization fall into a narrow range of ?3.0 to +2.6‰ with a mean of +0.1‰. The δ13CPDB values of dolomite and siderite from the Sawayaerdun gold deposit range from ?5.4 to ?0.6‰, possibly reflecting derivation of the carbonate carbon from a mixed magmatic/sedimentary source. Changes in physico‐chemical conditions and composition of the hydrothermal fluids, water–rock exchange and immiscibility of hydrothermal fluids are inferred to have played important roles in the ore‐forming process of the Sawayaerdun gold–antimony deposit.  相似文献   

19.
Shuiyindong is one of the largest and highest grade stratabound Carlin-type gold deposits in China. This paper reports on the results of petrographic studies, electron microprobe analyses (EMPA) of arsenian pyrite, and the mass transfer during mineralization and alteration, and it presents the deposit-scale distributions of Au, As, Sb, Hg, Tl, and trace elements in a representative cross section across the Shuiyindong Carlin-type gold deposit, Guizhou Province. The main objectives were to identify the precipitation mechanisms of minerals, or elements from fluids, and the migration paths of ore-forming fluids.Petrographic and EMPA studies indicate that gold in the primary ores is mainly hosted by arsenian pyrite. Mass transfer associated with alteration and mineralization shows that Au, As, Sb, Hg, Tl, and S were significantly added to all mineralized rocks, Fe2O3 and SiO2 were immobile in the main orebodies that are hosted in bioclastic limestone, and CaO, Na2O, Sr, and Li were removed from country rocks. The relations between Fe and S indicate that the sedimentary rocks at the Shuiyindong deposit contain more iron than is needed to combine with all of their contained sulfur to form pyrite. This suggests that sulfidation and decarbonation were the principal mechanism of gold precipitation at the Shuiyindong deposit. Hg, Sb, and As commonly formed sulfide minerals, such as stibnite, realgar, and orpiment, in late-stage quartz–calcite veins, or absorbed by organic matter in argillite. Fluid cooling presumably led to depositions of stibnite, realgar, and orpiment in late-stage quartz–calcite veins. Organic matter likely served as a reductant in argillite for the ore fluids, causing the precipitation of As, Sb, Hg, and S, as well as Au.Deposit-scale distributions of gold and other relevant elements reflect the passage of fluids through the rocks. Rock strata and structures allowed the ore-forming fluids to migrate horizontally along the unconformity surface of the Middle–Upper Permian, converge on the high position of an anticline, and then ascend into the overlying strata along the anticlinal axis. The distributions of the major and trace elements show that elements that accompanied the ore-forming fluids include Au, As, Sb, Hg, Tl, and S, and that Na2O and Li were exhausted in the Longtan Formation at the anticlinal core during gold mineralization. The enrichment of Co, Cr, and Ni in the Longtan Formation at the anticlinal core might be associated with deformation that formed the anticline, or with gold mineralization. Different host rocks were preferentially mineralized by different elements. The bioclastic limestone is commonly enriched in Au, whereas the argillite is preferentially enriched in As, Hg, Sb, and Tl. The zonation of ore-forming elements in the deposit appears to be Sb–Tl–As–Hg–Au–Hg–As (from bottom to top). Enrichment of Au, As, Sb, Hg, and Tl provides useful guidance for the exploration for Carlin-type gold deposits in Guizhou. Anomalies of As and Hg in soil or stream sediment might be an important clue and these elements can be used as indicator elements. Ore-forming fluids migrated along the unconformity surface of the Middle–Upper Permian and the anticlinal axis, so these are favorable sites for exploration for Carlin-type gold deposits in Guizhou.  相似文献   

20.
The Sandaowanzi gold-telluride deposit, with a total reserve of ?≥?25 t of Au and an average grade of 15 g/t, is located in the Great Hinggan Range Metallogenic Belt in NE China. This deposit is the first reported case of a dominantly Au (±Ag)-telluride deposit in this area and it reveals highly economic bonanza Au- and Ag-telluride ores. Ore bodies principally occur in quartz veins and stockworks and minor in disseminations hosted by trachyandesites and andesitic breccias. Four paragenetic stages of mineralization are identified, demonstrating an early deposition of sulfides and subsequent precipitation of tellurides, which are mainly composed by petzite, sylvanite and to a lesser extent, hessite, calaverite, altaite, unnamed telluride (Au1.8Ag0.2Te), krennerite, empressite, stützite and coloradoite. Abundant telluride assemblages identified from Sandaowanzi ores are mostly attributed to breakdown of early tellurium-bearing phases (i.e., γ- and χ-phases) during cooling. The deposition of substantial Au-Ag-Te minerals are constructed under physicochemical conditions of T?=?240 to 280 °C, pH?=?4.39 to 5.64, logfO2?=–44.8 to –41.8, logfTe2?=–9.75 to –9.43, logαAu+ (aq)/αAg+ (aq)?=??6.87 to –6.56, and gold is mostly scavenged from a HTe?-dominant ore-forming fluid. The unusually high Te concentrations in the Sandaowanzi epithermal system are likely attributed to alkaline to calc-alkaline magmatic degassing.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号