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1.
The Jupiter gold deposit in the northeastern Eastern Goldfields Province of the Yilgarn Craton of Western Australia is hosted
in greenschist facies metamorphosed tholeiitic basalt, quartz–alkali-feldspar syenite, and quartz–feldspar porphyry. Syenite
intrudes basalt as irregularly shaped dykes which radiate from a larger stock, whereas at least three E–W and NE–SW striking
quartz–feldspar porphyries intrude both syenite and basalt. Brittle–ductile shear zones are shallow-dipping, NW to NE striking,
or are steep-dipping to the south and west. Quartz ± carbonate veins that host gold at Jupiter occur in all lithologies and
are divided into: (1) veins that are restricted to the shear zones, (2) discrete veins that are subparallel to shear zone-hosted
veins, and (3) stockwork veins that form a network of randomly oriented microfractures in syenite wallrock proximal to shallow-dipping
shear zones. The gold-bearing veins comprise mainly quartz, calcite, ankerite, and albite, with minor sericite, pyrite, chalcopyrite,
galena, sphalerite, molybdenite, telluride minerals, and gold. Proximal hydrothermal alteration zones to the mineralised veins
comprise quartz, calcite, ankerite, albite, and sericite. High gold grades (>2 g/t Au) occur mainly in syenite and in the
hanging walls to shallow-dipping shear zones in syenite where there is a greater density of mineralised stockwork veins. The
Jupiter deposit has structural and hydrothermal alteration styles that are similar to both granitoid-hosted, but post-magmatic
Archaean lode-gold deposits in the Yilgarn Craton and intrusion-related, syn-magmatic, syenite-hosted gold deposits in the
Superior Province of Canada. Based on field observations and petrologic data, the Jupiter deposit is considered to be a post-magmatic
Archaean lode-gold deposit rather than a syn-intrusion deposit.
Received: 5 January 1999 / Accepted: 24 December 1999 相似文献
2.
Abstract. The Pongkor Gold‐Silver Mine, Bogor district, West Java, is approximately 80 km southwest of Jakarta. The gold and silver mineralization in the area is present in a deposit consisting of an epithermal vein‐system named individually as the Pasir Jawa, Gudang Handak, Ciguha, Pamoyanan, Kubang Cicau, and Ciurug veins. In the area studied, rocks of basaltic‐andesitic composition are dominated by volcanic breccia and lapilli tuff, with andesite lava and siltstone present locally. The hydrothermal alteration minerals in the Ciurug area are typical of those formed from acid to near‐neutral pH thermal waters, where the acid alteration is distributed from the surface to shallow depth, while the near‐neutral pH alteration becomes dominant at depths. The Ciurug vein shows four main mineralization stages where each discrete stage is characterized by a specific facies; these are, from early to late: carbonate‐quartz, manganese carbonate‐quartz, banded‐massive quartz and gray sulfide‐quartz facies. The major metallic minerals are pyrite, sphalerite, chalcopyrite and galena; they occur in almost each mineralization stage. Bornite was observed only in the southern part of the Ciurug vein at a depth of 515 m, and the occurrence of this mineral is reported here for the first time. Electrum and silver sulfides (mostly acanthite) are minor, whereas silver sulfosalts, stromeyerite and mckinstryite, and covellite are in trace amounts. The silver sulfosalts have compositional ranges of pearceite, antimon‐pearceite and polybasite. Most of the electrum occurs coexisting with other sulfide minerals, as inclusions in pyrite grains, with very little as inclusions in chalcopyrite or sphalerite. Gold grades within the Ciurug vein vary from 1.2 to hundreds of ppm, where the highest gold grade occurs in the latest mineralization stage in a thin sulfide band in vein quartz. Fluid inclusion microthermometry of calcite and quartz indicates deposition throughout the mineralized veins in the range from 170 to 230d?C and from low salinity fluids (predominantly lower than 0.2 wt% NaCl equiv.). Fluid inclusions occur with features of boiling. 相似文献
3.
The Pojeonri Cu quartz veins occur in the north-western portion of the Hwanggangri Metallogenic Province and consist of two parallel massive quartz veins that fill fractures oriented NW and NE along fault zones in Paleozoic metasedimentary and sedimentary rocks of the Ogcheon and Taebaeg belts. Based on the mineralogy and paragenesis of the veins, only one mineralization episode has been recognized. The ore minerals are mainly chalcopyrite, pyrrhotite, and pyrite with minor arsenopyrite, sphalerite, galena and oxides of those base metal minerals. 相似文献
4.
Hydrothermal quartz veins associated with gold and silver mineralization and variable amounts of base metal sulfides have been discovered within an active geothermal system in the Megala Therma area of northern Lesbos. This geothermal system is probably a late evolutionary stage in the formation of this mineralization. The veins are hosted in Upper Miocene volcanic rocks of andesitic composition and consist of quartz, adularia, chlorite, sericite, illite, kaolinite, baryte, small amounts of jarosite and alunite, and native gold, pyrite, galena, sphalerite, chalcopyrite, bornite, chalcocite, covellite and goethite. The principal types of alteration which occur in the studied area are: silicification, propylitization, argillic alteration and potassic, phyllic alteration. 相似文献
5.
The Jinwozi gold deposit consists of gold-bearing quartz veins in a biotite granodiorite of Hercynian age (zircon U-Pb age
≈ 335.7 Ma). Ore mineralogy is simple. In addition to native gold, there are only small amounts of sulfides, mainly pyrite
and minor sphalerite, chalcopyrite and galena. δ34S values average 6.69‰, and δ18O 13.99‰ Abundant CO2 is contained in fluid inclusions from quartz. Homogenization temperatures of fluid inclusions are between 186 and 262 °C.
REE distribution patterns indicate that the igneous mass may have been derived from a common initial material of calcareous-argillaceous
sediments and alkali basalts as the country rocks. In other words, the Jinwozi granodiorite is of remelting origin from crustal
material. Isotopic evidence of S, O and Pb shows that the ore-forming material is genetically related to magmatic hydrothermal
activity. 相似文献
6.
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.
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
8.
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
9.
Abstract: The gold deposit at Ashanti occurs in the Proterozoic Birimian formation of Ghana. Two main ore types mined from the deposit are gold-bearing quartz veins, and gold-sulfide disseminations in metasediments and metavolcanics. The main sulfide minerals in the gold-sulfide disseminated ores are arsenopyrite, pyrite and pyrrhotite, and to a very minor extent, sphalerite and tetrahedrite. Carbonate alteration and sericitization are prominent in the metavolcanics and the metasediments, respectively. In the quartz veins, pyrite and arsenopyrite commonly occur in small amounts, but gold mostly occurs in contact with tetrahedrite, chalcopyrite, galena, aurostibite, and sphalerite. Pyrrhotite is absent in the quartz veins.
Microprobe studies indicate that As content of homogeneous arsenopyrite grains ranges from 27. 0 to 31. 7 atm%, and gives mineralization temperatures from 170 to 430°C, although mostly from 300 to 400°C. Chlorite geothermometry using temperature dependence of substitution of Al for Si in the tetrahedral site gives formation temeratures of 330 to 400°C, comparable to the arsenopyrite temperatures. Applying sphalerite–pyrite–pyrrhotite geobarometry to sphalerite with FeS contents from 13. 6 to 12. 5 mol%, the pressure was estimated to be in a range from 5. 9 to 7. 0 kb at the stage of elevated temperatures.
Mineralogical observations, especially absence of pyrrhotite in the quartz veins, together with microprobe data for gold and associated minerals suggest that the fluids having ascended through fissures in the Ashanti deposit were reduced by the reaction with carbonaceous materials in the metasediments during the declining stage of the regional metamorphism. 相似文献
Microprobe studies indicate that As content of homogeneous arsenopyrite grains ranges from 27. 0 to 31. 7 atm%, and gives mineralization temperatures from 170 to 430°C, although mostly from 300 to 400°C. Chlorite geothermometry using temperature dependence of substitution of Al for Si in the tetrahedral site gives formation temeratures of 330 to 400°C, comparable to the arsenopyrite temperatures. Applying sphalerite–pyrite–pyrrhotite geobarometry to sphalerite with FeS contents from 13. 6 to 12. 5 mol%, the pressure was estimated to be in a range from 5. 9 to 7. 0 kb at the stage of elevated temperatures.
Mineralogical observations, especially absence of pyrrhotite in the quartz veins, together with microprobe data for gold and associated minerals suggest that the fluids having ascended through fissures in the Ashanti deposit were reduced by the reaction with carbonaceous materials in the metasediments during the declining stage of the regional metamorphism. 相似文献
10.
《Chemie der Erde / Geochemistry》2019,79(2):307-322
The Shurab Sb-polymetallic mineralization is a subvolcanic rock-hosted epithermal deposit and located in north Lut Block, eastern Iran. It is one of the most important deposits of the Iranian East Magmatic Assemblage (IEMA) in which numerous Middle-Cenozoic precious and base metals deposits occur. The main lithological units in the area are Paleogene subvolcanic intrusions and minor Jurassic sedimentary rocks. Mineralization occurs as veins in a series of NW-SE and E-W trending faults and fractures in the Eocene-Oligocene dacite and andesite subvolcanic rocks. Mineralization at the Shurab deposit can be subdivided into four stages: pre-ore stage, Cu-Zn-Pb ore stage, Sb-Ag ± As ore stage and post-ore stage. The total sulfide content of the veins in the area is variable, ranging from 1 to 50%, and is dominated by stibnite, chalcopyrite, galena, Fe-poor sphalerite and pyrite with minor chalcostibite, Ag-tetrahedrite and bournonite; gangue minerals are mainly quartz and calcite. Silicic, argillic, propylitic, and sericitic, are the most obvious wall rock alterations. Microthermometric measurements of primary liquid-rich fluid inclusions in quartz and sphalerite indicate that the veins were formed at temperatures between 115 and 290 °C from fluids with salinities between 0.7 and 16.2 wt% NaCl eq., suggesting an epithermal origin. The δ34S values of pyrite, chalcopyrite and galena vary between -2.5 and 0.8‰, and δ18O values of quartz range between 12.5 and 14.8‰. It is inferred that the Shurab mineralization is of epithermal origin, related to an Eocene-Oligocene magmatic geothermal system involving fluids of magmatic and meteoric origin. 相似文献
11.
The Huai Kham On gold deposit is located in the central part of the Sukhothai Fold Belt, northern Thailand. The Sukhothai Fold Belt represents an accretionary complex formed by subduction and collision between the Indochina and Sibumasu Terranes. There are many small gold deposits in the Sukhothai Fold Belt; however, the styles and formation environments of those gold deposits are not clear. The geology of the Huai Kham On deposit consists of volcanic and volcanosedimentary rocks, limestone, and low‐grade metamorphic rocks of Carboniferous to Triassic age. Gold‐bearing quartz veins are hosted by volcanic and volcanosedimentary rocks. The quartz veins can be divided into four stages. The mineral assemblage of the gold‐bearing quartz veins of Stages I and II comprises quartz, calcite, illite, pyrite, native gold, galena, chalcopyrite, and sphalerite. Quartz veins of Stage III consist of microcrystalline quartz, dolomite, calcite, pyrite, native gold, and chalcopyrite. Veins of Stage IV consist of calcite, dolomite, chlorite, and quartz. Fluid inclusions in quartz veins are classified into liquid‐rich two‐phase (Types IA and IB), carbonic‐aqueous (Type II), and carbonic (Type III) fluid inclusions. The homogenization temperatures of Types IA and II fluid inclusions that are related to the gold‐bearing quartz veins from Stages I to III ranged from 240° to 280°C. The δ18O values of quartz veins of Stages I to III range from +12.9 to +13.4‰, suggesting the presence of a homogeneous hydrothermal solution without temperature variation such as a decrease of temperature during the formation of gold‐bearing quartz veins from Stages I to III in the Huai Kham On gold deposit. Based on the calculated formation temperature of 280°C, the δ18O values of the hydrothermal solution that formed the gold‐bearing quartz veins range from +3.2 to +3.7‰, which falls into the range of metamorphic waters. The gold‐bearing quartz veins of the Huai Kham On deposit are interpreted to be the products of metamorphic water. 相似文献
12.
Detailed hydrothermal alteration investigations, including petrography, infrared reflectance spectroscopy (IRS) and XRD of the low sulfidation epithermal Co–O mine, located in Eastern Mindanao (Philippines) revealed that both distal and intermediate hydrothermal alteration zones contain dominantly illite and chlorite, whereas the proximal alteration zone comprises mainly illite, chalcopyrite and pyrite. The gold-bearing veins and the proximal hydrothermal alteration zone display a distinct absence of K-rich hydrothermal alteration minerals such as K-feldspar (adularia).Gold mineralization in the Co–O mine is controlled by an extensive quartz-breccia vein system, which is characterized by three distinct stages of vein (incl. breccias) formation. Gold is mainly observed in stages 2 and 3 veins. Stage 1 veins appear as fragments in stage 2 veins and display boiling textures such as quartz pseudomophs after bladed calcite. These veins further display colloform to crustiform banding and contain pyrite, chalcopyrite and minor gold located in the colloform bands and between bladed quartz pseudomorphs. Stage 2 veins comprise mostly banded to massive quartz and contains sulfides parallel to bands or disseminated. These veins are fine-grained with mosaic/jigsaw quartz and contain calcite blebs and/or fragments of stage 1 veins. Gold is in textural equilibrium with chalcopyrite, sphalerite, and locally pyrite. Stage 3 veins consist of quartz and carbonate (locally Mn-rich), and display irregular banded and comb textures. In auriferous veins of this stage gold is in textural equilibrium with chalcopyrite and pyrite (with local abundance of sphalerite). Other sulfide minerals observed with gold in stages 2 and 3 are galena, acanthite and locally jalpaite.The XRD and IRS provide inconsistent results regarding the abundance of K-rich clays (e.g., illite) associated with auriferous veins. Illite, with possibly interlayered swelling clays, such as Al-smectite, was identified in auriferous vein stages 2 and 3 using IRS, but could not be confirmed by XRD. Comparative analysis of the results of these techniques with respect to the ordering of micaceous minerals, suggest less ordered white mica proximal to the veins.Vein textures such as banded quartz, the absence of K-feldspar and the abundance of illite (interlayered Al-smectite) suggest relatively low temperatures of formation of the hydrothermal alteration system and point to a potential boiling horizon located deeper or marginal to the currently exploited levels of the Co–O mine. The absence of K-feldspar may also be related to relatively low temperatures of the hydrothermal fluid, the medium potassium-rich magma series of the host rocks, and/or a relatively low oxidation state of the hydrothermal fluid. 相似文献
13.
Oliver P. Kreuzer 《Mineralium Deposita》2006,40(6-7):639-663
Ore deposits of the Charters Towers Goldfield (CTGF) are mainly hosted by fault-fill veins. Extensional (∼8% of all veins) and stockwork-like (∼3%) veins are less common and of little economic significance. Crosscutting relationships and published structural and geochronological data indicate a Late Silurian to Early Devonian timing of gold mineralization, coincident with regional shortening (D4) and I-type magmatism. Paragenetic relationships, which are uniform in veins everywhere within the CTGF, suggest that vein formation commenced with the deposition of large volumes of buck quartz (stage I), followed by buck and comb quartz, and significant pyrite and arsenopyrite precipitation (stage II). Gold was introduced during stage III, after earlier sphalerite and coincident with galena and chalcopyrite. Narrow, discontinuous calcite veins of stage IV mark the waning of gold-related hydrothermal activity or a later unrelated episode. Ore zones within the veins are everywhere composed of comb and/or gray quartz, calcite and/or ankerite and bands or clusters of fractured pyrite that are spatially associated with galena, sphalerite or chalcopyrite. Low-grade or barren vein sections, on the other hand, are mainly composed of milky buck quartz with little evidence for modification, overprinting or interaction with later fluids. Gold-related hydrothermal wall-rock alteration is symmetrically zoned, displaying proximal sericite–ankerite and distal epidote–chlorite–hematite assemblages that may be taken to imply wall-rock interaction with near neutral fluids (pH 5–6). Isocon plots assuming immobile Al, P, Ti, Y and Zr consistently indicate As, K, Pb, S and Zn enrichment and Na, Si and Sr depletion in altered wall-rock specimens relative to the least altered rocks. Alteration assemblages, quartz textures, fault rocks and published fluid inclusion and stable isotope data imply that the veins were formed under conditions of episodic fluid overpressuring (∼0.9–3.8 kbar), at a depth of ∼7 km and a temperature of ∼310°C. The published fluid inclusion data also imply that gold precipitation may have been brought about by fluid mixing. However, physi- and chemisorption of gold complexes onto sulfide surfaces may have been important depositional processes and controls on gold enrichment at the millimeter to centimeter scale, given that most gold particles are attached to the surfaces of pyrite crystals of stage II or to etch-pits and fracture surfaces within the earlier pyrite. 相似文献
14.
Sajjad Maghfouri Ebrahim Rastad David R. Lentz Fardin Mousivand Flavien Choulet 《Chemie der Erde / Geochemistry》2018,78(1):40-57
The southwestern Sabzevar basin is the north of Central Iranian Microcontinent hosts abundant mineral deposits, including exhalative Mn mineralization and Cu-Zn volcanogenic massive sulfide (VMS) deposits. Amongst them, the Nudeh Besshi-type Cu–Zn volcanogenic massive sulfide (VMS) deposit is hosted within the lower part of a Late Cretaceous volcano-sedimentary sequence composed of alkali olivine basalt flows and tuffaceous silty sandstone. Based on investigations into the ore geometry, mineralogy, and texture, we recognized three different ore facies: (1) a stockwork of sulfide-bearing quartz veins cutting across the footwall volcano-sedimentary rocks and representing the stringer zone; (2) a massive ore type, displaying replacement texture with pyrite, chalcopyrite, sphalerite, friedrichite, and minor magnetite; and (3) a bedded ore type, with laminated to disseminated pyrite and chalcopyrite. EPMA studies indicate a distinctive minor element distribution between the different ore types of the Nudeh deposit. The Fe content in the sphalerite ranges from 0.65–1.80?wt.%, indicating the Fe-poor nature of the sphalerite. However, the Cd content in sphalerite ranged between 0.164–0.278?wt.%. According to the mineral compositions, Zn, Se, and Ag are found in bornite as minor elements. In the bedded ore facies, the pyrite contains higher levels of Se (up to 0.35?wt.%). The Zn content in the friedrichite in all of the ore samples is low. The Co/Ni ratios in pyrite from the Nudeh ore are lower than those of most magmatic deposits, but are similar to those from volcanogenic deposits, and hence support the proposed hydrothermal origin of the deposit. Two generations of quartz, Q1 and Q2 in the stockwork veins, contain primary fluid inclusions and these contain two phases (liquid and vapor). The lack of vapor-rich inclusions or variable liquid/vapor ratios indicate that the fluids did not boil at the site of trapping. Salinity for both Q1 and Q2 fluid inclusions ranges between 2.2–6.8?wt.% eq. NaCl. Homogenization temperatures for inclusions in the Q1 and Q2 veins average at about 296?°C and are similar to the temperatures of hydrothermal fluids discharged through vents in many modern seafloor VMS deposit. The Nudeh Besshi-type VMS deposit appears to have formed on the seafloor and based on the salinity and temperature constraints from the underlying stockwork, a buoyancy plume model is proposed as a mechanism for precipitation. 相似文献
15.
Gold mineralisation in the White River area, 80 km south of the highly productive Klondike alluvial goldfield, is hosted in
amphibolite facies gneisses in the same Permian metamorphic pile as the basement for the Klondike goldfield. Hydrothermal
fluid which introduced the gold was controlled by fracture systems associated with middle Cretaceous to early Tertiary extensional
faults. Gold deposition occurred where highly fractured and chemically reactive rocks allowed intense water–rock interaction
and hydrothermal alteration, with only minor development of quartz veins. Felsic gneisses were sericitised with recrystallisation
of hematite and minor arsenic mobility, and extensively pyritised zones contain gold and minor arsenic (ca 10 ppm). Graphitic
quartzites (up to 5 wt.% carbon) caused chemical reduction of mineralising fluids, with associated recrystallisation of metamorphic
minerals (graphite, pyrrhotite, pyrite, chalcopyrite) in host rocks and veins, and introduction of arsenic (up to 1 wt.%)
to form arsenopyrite in veins and disseminated through host rock. Veins have little or no hydrothermal quartz, and up to 19 wt.%
carbon as graphite. Late-stage oxidation of arsenopyrite in some graphitic veins has formed pharmacosiderite. Gold is closely
associated with disseminated and vein sulphides in these two rock types, with grades of up to 3 ppm on the metre scale. Other
rock types in the White River basement rocks, including biotite gneiss, hornblende gneiss, pyroxenite, and serpentinite, have
not developed through-going fracture systems because of their individual mineralogical and rheological characteristics, and
hence have been little hydrothermally altered themselves, have little hydrothermal gold, and have restricted flow of fluids
through the rock mass. Some small post-metamorphic quartz veins (metre scale) have been intensely fractured and contain abundant
gold on fractures (up to 40 ppm), but these are volumetrically minor. The style of gold mineralisation in the White River
area is younger than, and distinctly different from, that of the Klondike area. Some of the mineralised zones in the White
River area resemble, mineralogically and geochemically, nearby coeval igneous-hosted gold deposits, but this resemblance is
superficial only. The White River mineralisation is an entirely new style of Yukon gold deposit, in which host rocks control
the mineralogy and geochemistry of disseminated gold, without quartz veins. 相似文献
16.
The study of solid mineral inclusions in detrital hydrothermal and hydrothermally altered zircons and quartz from Archaean and Palaeoproterozoic (Sumian and Jatulian) terrigenous quartz-rich clastic rocks of the Karelian Craton on a VEGA II LSH-TESKAN microanalyzer has revealed, for the first time, micron-sized native gold inclusions and associated syngenetic inclusions of ore minerals, such as galena, sphalerite, pyrite, chalcopyrite, molybdenite, molybdoscheelite, native bismuth and cerussite, as well as barite and complex hydroaluminophosphates of the goyacite-gorceixite-florencite-plumbogummite group. This mineral association in detrital material could indicate the ore-forming nature of its quartz vein source. These data, together with the earlier results of the local isotopic (SHRIMP-II and LA-ICP-MS) dating of these and similar heterogeneous detrital zircons, are indicative of several hydrothermal events, dated at 3.3, 3.15?C2.9 and 2.76?C2.65 Ga, which occurred in the region in Archaean time. The two latter ages are consistent with the time of formation of quartz vein ore systems with some of which gold ore-forming processes were associated. 相似文献
17.
18.
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
19.
Ore minerals and geochemical characterization of the Dungash gold deposit,South Eastern Desert,Egypt
Islam A. Dourgham Khairiya M. Fawzy Hartwig E. Frimmel 《Arabian Journal of Geosciences》2017,10(6):145
The Dungash historic gold mine is located in the South Eastern Desert of Egypt. The gold-bearing quartz veins are hosted by the metavolcanic and metavolcaniclastic rocks along an ENE–WSW trending shear zone. Alteration types recorded in the wall rocks are sericitization, silicification, carbonatization, chloritization, sulfidization, ferruginization, and listwanitization. The ore mineral assemblage comprises arsenopyrite, pyrite, native gold, pyrrhotite, sphalerite, chalcopyrite, and galena. The primary sulfide mineral assemblage formed during a hypogene hydrothermal stage whereas anglesite and goethite occur as secondary supergene phases. Microthermometric fluid inclusion analysis revealed that the auriferous quartz precipitated from a moderately saline (5 to 11.22 wt% NaClequiv) solution at temperatures above the recorded homogenization temperatures (T h), which range from 380 to 177 °C. The minimum pressures of trapping are between 350 and 400 bars. The fluid evolution during mineralization is explained by mixing of a magmatic fluid with meteoric waters. Initially, the high temperature and moderately saline magmatic fluid dominated and progressively became diluted with meteoric waters. Highest gold content is recorded in the carbonatized zone and the quartz veins. However, gold content in the carbonatized zone of the footwall exceeds several times its content in the quartz veins and the carbonatized zone of the hanging wall. 相似文献
20.
Jonelle Nikolai Crisostomo Jeddalyn Parian Daizo Ishiyama Redempta Baluda Sonia Eguia Jocelyn Galapon Gerry Comia Jessie Segura Maureen Laroco Noel Oliveros Victor B. Maglambayan 《Resource Geology》2007,57(2):241-247
Two ore and three alteration types were identified in the Lascogon Project of Philex Gold Philippines, in Surigao del Norte, Mindanao Island, Philippines. The jasperoid ore is the host to the Carlin‐like gold mineralization in the Lascogon and Danao prospects. The ore occurs in a decalcified and silicified horizon, with minor chlorite and goethite, stibnite, pyrite and quartz crystals ranging from cryptocrystalline to botryoidal. The stringer–stockwork type Cu‐Au mineralization in the Suyoc prospect is hosted in argillized andesitic rocks of the Mabuhay Formation. The primary ore minerals are chalcopyrite with minor amounts of sphalerite. The alteration types identified are propylitic alteration, argillic alteration and silicification. The propylitized basaltic and andesitic flows of the Bacuag Formation bound the jasperoid mineralization in the Lascogon prospect. Stratigraphically, the relationship between propylitized basalts and stringer–stockwork Cu‐Au is not clear but a lateral change can be inferred from jasperoid in the center and stringer–stockwork towards the east. 相似文献