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1.
The C. S. A. Mine is located near Cobar, central New South Wales. The copper-zinc-lead ores occur in Early Devonian rocks of the Cobar Super-Group. Lower greenschist (slate-grade) metamorphism has developed elongate lenticular ore systems parallel to the extension (down-dip) lineation in cleavage. FeS contents of sphalerites coexisting with pyrite and pyrrhotite outside and inside pressure shadows indicate much higher pressures (7.7 to 9.0 kbar) than those inferred from stratigraphic reasoning and the low metamorphic grade. The homogeneous distribution of Fe in sphalerites suggests equilibration with pyrite-pyrrhotite; and concentrations of Co and Ni in iron sulphides, and Mn, Cd and Cu in sphalerite are too low to have influenced phase relations in the FeS-ZnS pseudobinary system. The anomalously high pressures are therefore ascribed to reequilibration of sphalerite compositions with a monoclinic pyrrhotite-pyrite buffer. The FeS contents of the reequilibrated sphalerites apparently reflect the differing mean stress domains that exist outside and inside pressure shadows. This suggests that reequilibration occurred under the same stress distribution as produced the original pressure shadows, and implies FeS dissolution during the decay of the cleavage-producing structuro-metamorphic event. The commonly observed scatter of sphalerite compositions in low grade assemblages appears to record micro-scale mean stress domains, and thereby testifies to the pressure sensitivity of the mole percent FeS contents. 相似文献
2.
H. H. STOWELL 《Journal of Metamorphic Geology》1989,7(3):343-358
ABSTRACT The western metamorphic belt of the Coast Plutonic Complex, south-east Alaska and adjacent British Columbia, contains strongly deformed rocks and a prominent topographic low: the Coast Range megalineament. Near Holkham Bay, south-east Alaska, the lineament separates the western metamorphic belt into: a western low-grade (greenschist facies) terrane, and an eastern medium-grade (amphibolite facies) terrane. Sphalerite compositions of grains in direct contact with pyrite and pyrrhotite in chlorite-muscovite zone rocks in the low-grade terrane give pressures of about 8 kbar; compatible with pressures of 8-10 kbar at 500°C calculated from plagioclase-biotite-garnet-muscovite assemblages adjacent to the Windham Bay pluton about 15 km away. A pressure of 4.8 ± 0.7 kbar was calculated from sphalerite compositions in staurolite zone rocks east of the Coast Range megalineament. This is indistinguishable from pressures of 4.8 ± 1 kbar at 585°C and 5.1 ± 1 kbar at 680°C (plagioclase-garnet-aluminum silicate-quartz equilibria), and 4.1 ± 1 kbar at 585°C (plagioclase-biotite-garnet-muscovite equilibrium) determined for the medium-grade terrane. An identical pressure of 4.8 ± 0.7 kbar was calculated from sphalerite compositions in biotite zone rocks adjacent to the lineament; this is considerably higher than a pressure of 3.1 ± 1 kbar at 525°C obtained using plagioclase-biotite-garnet-muscovite geobarometry from shear zones within the lineament. The discrepancy may be explained by later equilibration of mineral phases within the shear zones. The geothermobarometry suggests relatively low temperatures and high pressures for the low-grade terrane (6-10 kbar), and intermediate temperatures and pressures for the medium-grade terrane to the east (4-6 kbar). Comparison of the barometers indicate that sphalerite can be used to estimate metamorphic pressures, similar to those estimated from silicate mineral chemistry when pyrrhotite-sphalerite-pyrite assemblages are used. 相似文献
3.
Based on the equation recently determined, formation pressures of skarn-type ore deposits were estimated from the composition of sphalerite coexisting with pyrite and hexagonal pyrrhotite. As criteria for equilibrium among sphalerite, pyrite and hexagonal pyrrhotite, the following three points were carefully checked on each specimen: 1) the presence of hexagonal pyrrhotite, 2) no time sequences among the formation of sulfide minerals, and 3) no compositional variation in sphalerite. Most of the Cu-Fe skarn deposits studied were formed under pressures of more than 1 kb, whereas Zn-Pb(-Cu-Fe) deposits tend to have formed at relatively shallow environments, namely under less than 1 kb. The calculated pressures are qualitatively consistent with the depth of formation of deposits estimated from the geological evidences. The sphalerite geobarometry is quite sensitive even at low pressure ranges, and it is applicable to the deposits formed under shallow conditions. 相似文献
4.
In the Ospin–Kitoi ultramafic massif of the Eastern Sayan, accessory and ore Cr-spinel are mainly represented by alumochromite and chromite. Copper–nickel mineralization hosted in serpentinized ultramafic rocks occurs as separate grains of pentlandite and pyrrhotite, as well as assemblages of (i) hexagonal pyrrhotite + pentlandite + chalcopyrite and (ii) monoclinal pyrrhotite + pentlandite + chalcopyrite. Copper mineralization in rodingite is presented by bornite, chalcopyrite, and covellite. Talc–breunnerite–quartz and muscovite–breunnerite–quartz listvenite contains abundant sulfide and sulfoarsenide mineralization: pyrite, gersdorffite, sphalerite, Ag–Bi and Bi-galena, millerite, and kuestelite. Noble metal mineralization is represented by Ru–Ir–Os alloy, sulfides, and sulfoarsenides of these metals, Au–Cu–Ag alloys in chromitite, laurite intergrowth, an unnamed mineral with a composition of Cu3Pt, orcelite in carbonized serpentinite, and sperrylite and electrum in serpentinite. Sulfide mineralization formed at the late magmatic stage of the origination of intrusion and due to fluid–metamorphic and retrograde metasomatism of primary rocks. 相似文献
5.
Evidence for,and implications of,a primary FeS phase in the lead-zinc bearing sediments at Mount Isa
Quantitative mineral data from the lead-zinc bearing sediments at Mount Isa were studied using linear correlation analysis and R-mode cluster analysis. Pyrrhotite was found to be preferentially associated with galena and sphalerite. It is postulated that during sedimentation, formation of lead and zinc sulphides depleted an already limited sulphur supply to the point where the field of FeS stability was entered. The primary iron monosulphide formed was, or has since become, pyrrhotite. This hypothesis is in contrast to the widely held opinion that pyrrhotite in stratiform ores formed by metamorphic decomposition of pyrite. Empirical support for the sedimentary formation of pyrrhotite is provided by textural and qualitative mineralogical data from Mount Isa and other stratiform lead-zinc deposits. 相似文献
6.
The New Consort Gold Mine in the Palaeo- to Mesoarchaean Barberton greenstone belt, South Africa is one of the oldest recognized
orogenic gold deposits on Earth. The gold mineralization is hosted by discrete mylonitic units that occur at, or close to,
the contact between the mafic and ultramafic volcanic rocks of the c. 3,280 Ma Onverwacht Group and the mainly metasedimentary
rocks of the overlying c. 3,260–3,230 Ma Fig Tree Group. This contact, locally referred to as the Consort Bar, formed during
ductile D1 imbrication of the metavolcanosedimentary sequence and predates the main stage of the gold mineralization. The imbricate
stack is situated in the immediate hanging wall of the basal granitoid–greenstone contact along the northern margin of the
greenstone belt. It is characterized by a condensed metamorphic profile in which the metamorphic grade increases from upper
greenschist facies conditions (510–530°C, 4 kbar) in rocks of the Fig Tree Group to upper amphibolite facies grades (600–700°C,
6–8 kbar) in the basal Onverwacht Group. Detailed structural and petrological investigations indicate that the Consort Bar
represents a major structural break, which is largely responsible for the telescoping of metamorphic isograds within the structural
sequence. Two stages of mineralization can be distinguished. Loellingite, pyrrhotite, and a calc–silicate alteration assemblage
characterize an early high-T mineralization event, which is restricted to upper amphibolite facies rocks of the Onverwacht
Group. This early mineralization may correlate with the local D1 deformation. The second and main stage of gold mineralization was associated with renewed ductile shearing during D2. The D2 deformation resulted in the reactivation of earlier structures, and the formation of a NNW trending, steeply dipping shear
zone system, the Shires Shear Zone, which separates two regional SE plunging D1 synclines. The mineralized shear zones are intruded by abundant syn-kinematic pegmatite dykes that have previously been dated
at c. 3040 Ma. Petrological and geothermobarometric data on ore and alteration assemblages indicate that the main stage of
gold mineralization, which affected a crustal profile of ca. 1.5 km, was characterized by increasing temperatures (c. 520
to 600°C) with increasing structural depth. Sulfide assemblages in the ore bodies change progressively with metamorphic grade,
ranging from arsenopyrite + pyrite + pyrrhotite in the structurally highest to arsenopyrite + pyrrhotite + chalcopyrite +
loellingite in the structurally deepest part of the mine. The main stage of gold mineralization was broadly syn-peak metamorphic
with respect to the Fig Tree Group, but postdates the peak of metamorphism in upper amphibolite facies rocks of the structurally
underlying Onverwacht Group. This indicates that the mineralization coincided with the juxtaposition of the two units. As
the footwall rocks were already on their retrograde path, metamorphic devolatilisation reactions within the greenstone sequence
can be ruled out as the source of the mineralizing fluids. 相似文献
7.
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
8.
Development of inverted metamorphic isograds in the western metamorphic belt, Juneau, Alaska 总被引：3，自引：0，他引：3
An inverted metamorphic gradient is preserved in the western metamorphic belt near Juneau, Alaska. The western metamorphic belt is part of the Coast plutonic–metamorphic complex of western Canada and southeastern Alaska that developed as a result of tectonic overlap and/or compressional thickening of crustal rocks during collision of the Alexander and Stikine terranes. Detailed mapping of pelitic single-mineral isograds, systematic changes in mineral assemblages, and silicate geothermometry indicate that thermal peak metamorphic conditions increase structurally upward over a distance of about 8 km. Peak temperatures of metamorphism increase progressively from about 530 °C for the garnet zone to about 705 °C for the upper kyanite–biotite zone. Silicate geobarometry suggests that the thermal peak metamorphism occurred under pressures of 9–11 kbar. The metamorphic isograds are in general parallel to the tonalite sill that is regionally continuous along the east side of the western metamorphic belt, although truncation of the isograds north of Juneau indicates that the sill intrusion continued after the isograds were established. Our preferred interpretation of the cause of the inverted gradient is that it formed during compression of a thickened wedge of relatively wet and cool rocks in response to heat flow associated with the formation and emplacement of the tonalite sill magma. Garnet rim compositions and widespread growth of chlorite suggest partial re-equilibration of the schists under pressures of 5–6 kbar during uplift in response to final emplacement and crystallization of the tonalite sill. The combined results of this study with previous studies elsewhere in the western metamorphic belt indicate that high-T/high-P metamorphism associated with the collision of the Alexander and Stikine terranes was a long-lived event, extending from about 98 Ma to about 67 Ma. 相似文献
9.
The compositions of arsenopyrite and sphalerite from five Swedish metamorphosed Cu, Zn-sulfide deposits are related to T and P, according to the methods described by Kretschmar and Scott (1976) and Scott (1973). The As/S ratio of arsenopyrite indicates an equilibrium temperature around 400°C for all the deposits studied, whereas the sphalerite barometer shows pressures between 5 and 7 kb. The mineral assemblages of the bedrocks indicate a similar temperature but a lower pressure. A constant fs2 is probably only effective over distances of millimetres or a few centimetres in the samples studied. The fs2 has always been lower in the surrounding rocks than in the ores as indicated by a higher As/S in arsenopyrite, more FeS in sphalerites and the absence of pyrite. 相似文献
10.
Several important mineral deposits of Sn, Zn, Cu, Pb, and other metals associated with Devonian sediments and Yanshanian (Cretaceous) granitic rocks are known in the Dachang district (Guangxi). Early genetic hypotheses related the origin of the deposits entirely to the Yanshanian granites. Recently, it was suggested that in Devonian times an earlier syngenetic metal concentration may have occurred, later overprinted by the Yanshanian metallogeny. This contribution is aimed at placing constraints on the physicochemical conditions during the Yanshanian ore formation-remobilization by studying the sulfide chemistry (arsenopyrite, sphalerite, stannite) and fluid inclusion data on the two major deposits in the area, i.e., the polymetallic cassiterite deposit of Changpo and the Zn-Cu skarn deposit of Lamo. Sphalerite and arsenopyrite are quite abundant in both deposits; stannite is minor, but fairly widespread at Changpo, and quite rare at Lamo. They are accompanied by pyrite, pyrrhotite, galena, chalcopyrite, cassiterite, fluorite, and a large variety of other sulfides and sulfosalts. The main compositional data for sphalerite and arsenopyrite are summarized as follows:Changpo: arsenopyrite associated with pyrrhotite 31.4–36.1 at% As; Associated with pyrite 31.9–33.1 at% As; sphalerite associated with pyrrhotite 18.3–22.2 mol% FeS; associated with pyrite 10.6–18.6 mol% FeS.Lamo: arsenopyrite associated with pyrrhotite 32.9–35.3 at% As; associated with pyrite 30.3–31.7 at% As; sphalerite associated with pyrrhotite, 17.2–24.4 mol% FeS; associated with pyrite 4.2–19.6 mol% FeS.Partitioning of Fe and Zn between coexisting sphalerite and stannite from Changpo indicates temperatures of 300°–350°C. For Lamo, the following fluid inclusion data are available: fluorite, salinities of 0–9.5 equiv. wt% NaCl, and homogenization temperatures between 160°C and 250°C; quartz, moderate salinities (0–4.6 equiv. wt% NaCl), and homogenization temperatures of 208°–260°C. Combining the mineralogical evidence with the compositional and fluid inclusion data, it is suggested that the evolution of the environment during the Yanshanian event was characterized by the following parameters: pressure was relatively low (on the order of 1–1.5 kb); temperature may have been as high as 500°C during deposition of the As-richest arsenopyrites, but eventually dropped below 200°–250°C in the latest stages; with an increase in sulfur activity and/or the decrease in temperature pyrrhotite was no longer stable in the latest stages of mineralization. 相似文献
11.
通过对热液脉型的铅－锌－银矿床（３个）和银矿床（１个）和闪锌矿中硫化物包囊体的特征研究表明,石英－硫化物阶段富铁闪锌矿（主矿物）的硫化物包裹体十分发育：沿生长带产出的乳滴状黄铜矿与主矿物为共同沉淀成因;沿穿切主矿物的黄铜矿或石英细脉两侧,和受粗粒黄铜矿溶蚀的富铁闪锌矿近接触部位发育的乳滴状黄铜矿为渗透－交代产物;沿解理（裂隙）或粒间、粒内产出的各种形态磁黄铁矿是充填－交代的结果;沿解理分布的脉状毒 相似文献
12.
W. R. Ryall 《Mineralium Deposita》1981,16(3):425-435
Mercury concentrations of four Australian stratiform lead-zinc-silver deposits of Proterozoic age are not directly related to their metamoprhic grade and are probably determined by local factors. Average mercury contents of H. Y. C. mineralization (unmetamorphosed) is 1300 ppb, Mount Isa ore (greenschist facies) 8300 ppb, Squirrel Hills mineralization (amphibolite facies) 100 ppb, and Broken Hill ore (granulite facies) ranges from 1000 ppb for A lode to 37000 ppb for No. 3 lens. In present-day sulfidic muds from the Coorong region of South Australia, mercury is present as mercury sulfide either as inclusions or chemisorbed on mackinawite. This may be analogous to the manner of mercury occurrence in sediments which predated the ingress of lead-zinc-silver mineralization into ancient basins. In bedded H. Y. C. mineralization mercury is present principally in pyrite, but recrystallized mineralization contains mercury in both sphalerite and pyrite. In bedded Mount Isa ore mercury is present in sphalerite, but in remobilized ore which is enriched in galena, freibergite and pyrrhotite, it occurs in both sphalerite and freibergite. Mineralization from Squirrel Hills contains no tetrahedrite, and sphalerite is the host for most mercury. Normal Broken Hill ore contains mercury parti tioned approximately evenly between sphalerite and tetrahedrite, but mercury is enriched in remobilized ore. Veins generated during retrograde metamorphism of the Broken Hill lodes contain high levels of mercury, and multiple veins produced in this fashion around other deposits could result in mercury haloes that can be detected during exploration programs. The way mercury is held in stratiform leadzinc-silver deposits, and the lack of decrease of mercury contents with increasing metamorphic grade, rules out total loss of mercury during metamorphism. Primary mercury haloes around this type of mineralization are due to mercury in disseminated ore-forming minerals or late-stage vein systems contain secondary mercury-bearing minerals. 相似文献
13.
Contrasting sapphirine parageneses from Wilson Lake, Labrador and their tectonic implications 总被引：7，自引：0，他引：7
Abstract Regionally distributed pelitic granulites in the Wilson Lake region contain the assemblage sapphirine + hypersthene + sillimanite + quartz. Geochronology and geobarometry suggest it developed in early Proterozoic rocks at temperatures approaching 900°C and pressures above 10 kbar. Vein-like metasomatized rocks around a suite of mafic to ultramafic intrusions, emplaced near the peak of metamorphism about 1700 Ma ago, contain sapphirine, but these assemblages developed at temperatures near 750°C and pressures of 4.5 kbar. Both types of assemblage occur as relics in amphibolite-grade (biotite–sillimanite) migmatites.
P–T determinations indicate rapid isothermal uplift of 20 km accompanied by mafic intrusion and hydration. The metamorphic history and tectonic setting suggest exposure of deep continental crust by thrusting during continental collision, followed by essentially isothermal decompression. 相似文献
P–T determinations indicate rapid isothermal uplift of 20 km accompanied by mafic intrusion and hydration. The metamorphic history and tectonic setting suggest exposure of deep continental crust by thrusting during continental collision, followed by essentially isothermal decompression. 相似文献
14.
15.
对云南、海南、江西、湖北、河南、新疆、浙江、山东、辽宁等27个省185个典型金矿床的自然重砂矿物进行统计分析,发现自然重砂矿物对金矿具有良好的响应,自然金、黄铁矿、方铅矿、黄铜矿、白铅矿、辰砂等对寻找金矿具有指示意义。不同成因类型的金矿床反映出的自然重砂矿物组合不同,斑岩型金矿床的标型指示矿物组合为自然金+黄铁矿+方铅矿+重晶石+闪锌矿+白铅矿+金红石,卡林型—类卡林型金矿床的标型指示矿物组合为自然金+黄铁矿+方铅矿+辉锑矿+毒砂+雄(雌)黄,而造山型+矽卡岩型+热液型+构造蚀变岩型金矿床的标型指示矿物组合为自然金+黄铁矿+方铅矿+辰砂。不同区域的金矿床反映出的自然重砂矿物组合也各有差异,闪锌矿为南方各省金矿床的特征矿物,辰砂和白钨矿为北方地区金矿床的特征矿物,重晶石和白铅矿为西部地区金矿的特征矿物。综合研究认为,自然重砂具有直接找矿和指导找矿的作用,按照特定成因类型和区域金矿床所建立的自然重砂矿物组合对建立矿床找矿模型具有重要的意义。 相似文献
16.
我国是世界上最大的铜精矿进口国,研究不同产地铜精矿的矿物学特征,能支撑铜精矿原产地分析及相关固体废物属性鉴定。本文研究对象为来自8个国家12个矿区的进口铜精矿样品,采用X射线荧光光谱(XRF)、X射线粉晶衍射(XRD)以及偏光显微镜进行综合分析,探寻这些矿区铜精矿的元素组成、矿物组合特征,探讨不同成因类型铜精矿的矿物学差异。X射线荧光光谱分析表明铜精矿样品主要元素为Cu、Fe、S、O,普遍含有Zn、Si、Al、Mg、Ca、Pb;X射线粉晶衍射物相分析表明铜精矿样品主要物相为黄铜矿,其次常含有黄铁矿和闪锌矿等物相;偏光显微镜光片鉴定表明铜精矿样品金属矿物中黄铜矿的含量在88%~98%之间,观察到黄铜矿与闪锌矿、黄铁矿、磁黄铁矿共生,闪锌矿与斑铜矿、砷黝铜矿共生,黄铜矿、砷黝铜矿和斑铜矿共生等连生体矿相。结合铜精矿不同成矿类型分析表明,斑岩型、矽卡岩型、火山成因块状硫化型铜矿床样品中常见黄铜矿、黄铁矿、闪锌矿,并分别含有黑云母、草酸钙石、硫酸铅特征矿物;铁氧化物铜金矿床样品主要矿物为黄铜矿,常见磁黄铁矿、滑石特征矿物。通过本文采用多种技术表征不同产地铜精矿样品元素含量、物相组成、矿相组成的差异,能够全面分析不同产地铜精矿样品的矿物学特征,对进口铜精矿的风险识别和管控具有重要意义。 相似文献
17.
The high-temperature (HT) to ultrahigh-temperature (UHT) metamorphic rocks from Lützow–Holm Complex, East Antarctica show a systematic difference between sulfide assemblages in the rock matrix and those found as inclusions in the silicates stable in high-temperatures. Matrix sulfides are commonly pyrite with or without pentlandite and chalcopyrite. On the other hand, inclusion sulfides are pyrrhotite with or without pentlandite and chalcopyrite lamellae. When recalculated into integrated single-phase sulfide compositions, inclusion sulfides from the UHT region showed a wider range of solid–solution composition than the inclusion sulfides from the HT region. The host minerals of the sulfides with extreme solid–solution compositions are those stable at the peak of metamorphism such as orthopyroxene and garnet. One of the most extreme ones is included in orthopyroxene coexisting with sillimanite ± quartz, which is the diagnostic mineral assemblage of UHT metamorphism. These observations suggest that sulfide inclusions preserve their peak metamorphic compositions. Pyrrhotite did not revert to pyrite because of the closed system behavior of sulfur in inclusion sulfides. On the other hand, in the rock matrix where the open system behavior of sulfur is permitted, original sulfides were partly to completely altered by the later fluid activity. 相似文献
18.
Yuanchuan ZHENG Lianxing GU Xiaoqian TANG Zijiang WANG Changzhi WU Wenlan ZHANG Xueyi WU 《Resource Geology》2012,62(2):174-186
We conducted experiments to simulate sulfide remobilisation from sulfide ore. The starting material was from the Hongtoushan massive sulfide deposit, NE China, and is composed of pyrite, pyrrhotite, chalcopyrite, sphalerite, quartz, and silicate minerals. The ore was immersed in a solution of 20 wt.% NaCl for 260 h, and then was mounted in a Changjiang 500 triaxial rock stress machine. After the experiments were performed for 13 h at temperatures of 362, 464, 556 and 682°C, with corresponding confining and axial pressures, the samples were cooled at room temperatures. Our results from all the runs indicate that sulfides can be remobilised both mechanically and chemically, and that remobilisation is enhanced at higher temperatures. Mechanical remobilisation can only take place over limited distances and results in minor differentiation between various sulfide minerals. Distant external remobilisation to form new orebodies is most likely caused by chemical remobilisation. In contrast to plastically deformed areas, space resulting from cataclastic deformation could provide conduits for fluid transport and space for metal precipitation. Remobilised iron sulfides will precipitate as pyrrhotite at high temperatures, but as pyrite when temperature decreases. Furthermore, chalcopyrite is more easily remobilised than sphalerite under the conditions of the present experiments. Remobilisation accompanying deformation and metamorphism may add epigenetic features to syngenetic deposits. 相似文献
19.
WilliamS.FYFE 《《地质学报》英文版》1999,73(1):1-7
The Jiaodong gold province is situated in the eastern Sino-Korean Platform within the so-calledJiaoliao Uplift. The basement rocks are Archaean and Proterozoic metamorphic rocks. Mesozoic sedimentary andvolcanic cover occur within extensional basins. Intrusive rocks are dominated by Mesozoic granitoid, with interme-diate-acid and basic dyke swarms. The structures form an E-W-trending anticlinorium in the basement complex, andlarge-scale NE-SW-and NNE-SSW-trending fault zones of Mesozoic age. The gold mineralization is associated withthe Mesozoic faults and related secondary fractures in the granites or granite-basement contacts. The mineralizationtypes are quartz-vein type and wall-rock alteration type. Wall-rock alteration is very well developed around the orezones. Alteration minerals include quartz, sericite (and fuchsite), pyrite, calcite, chlorite, hematite, rutile and graph-ite. The ore assemblage is uniform in all deposits, including pyrite, chalcopyrite, galena, sphalerite, arsenopyrite,pyrrhotite, gold, electrum, hessite, petzite, magnetite, molybdenite, tetrahedrite and wolframite. Mesozoic collisionand subduction between the South China and North China continental blocks contributed to formation of the Meso-zoic granitoid intrusions. The granitic magma is considered to be derived from partial melting of the crust throughunderplating processes. Gold was remobilised from basement rocks and deposited in fracture zones by the high-temperature fluids associated with these processes. 相似文献
20.
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