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1.
In surface environments, placer gold particles are (re)shaped by physical, chemical and biogeochemical processes. This study hypothesizes that in modern landscapes combinations of physical and biogeochemical factors determine placer gold transformation and the composition of biofilm communities living on particle surfaces. Morphology, composition and biofilm communities of placer particles from eight locations in Switzerland were analyzed. Sites reflect a variety of modern-day placer environments in mountainous terrains, ranging from eluvial sites in close proximity to primary sources, to alluvial sites associated with both slow- and fast-moving streams, and to distal glacio-fluvial and depositional lake sediments. Particles are progressively physically and biogeochemically transformed with increasing distance from source. Variable degrees of rounding, gouging and scratching from physical reshaping due to transport and sedimentation processes are evident especially on particles from high energy environments. Surface textures indicative of biogeochemical gold/silver dissolution are common. In low energy/depositional environments and with increasing distance from source overgrowths of gold nano- and micro-particles and aggregates are abundant. These form micro-crystalline layers of secondary gold on particle surfaces covering them to depths of tens of micrometers. Biofilm communities across all sites are dominated by Proteobacteria (669 Operational Taxonomic Units (OTUs), 49.8%), especially β‑Proteobacteria. Other important phyla include Acidobacteria, (172 OTUs, 9.7%), Bacteroidetes (222 OTUs, 11.6%), Cyanobacteria (26 OTUs, 13.7%), and Planctomycetes (125 OTUs, 7.1%). Canonical analysis of principal coordinates demonstrates significant links of community assemblages to biogeochemical transformation and landscape position of collected particles. Increasing specialization towards metallophilic phyla was recorded on particles collected with increasing distance from source, suggesting that Au toxicity resulting from progressing biogeochemical transformation affected bacterial communities. This study ultimately shows that placer gold transformation and biofilm composition within modern landscapes is highly dependent on the interplay of physical and biogeochemical factors. 相似文献
2.
Placer gold particles derived from epithermal deposits display distinct morphological and compositional features compared with particles from mesothermal systems. Here, it is hypothesized that the chemical composition of primary gold derived from different deposit types is a principle factor affecting the composition of resident biofilm communities as well as the transformation of placer particles. Gold particles were collected from placers originating from the epithermal system at the Eisenberg, Germany's largest primary gold deposit. For comparison, placer gold from mesothermal sources was studied. Morphological differences due to mechanical transport and physical reshaping were not observed. Biogeochemical gold/silver dissolution and gold re-precipitation were evident on epithermal particles and they accentuate the silver-fabrics and gold-rich clusters. In contrast, on mesothermally derived gold particles these processes led to the development of gold-rich rims via the formation of nano-porous secondary gold. Microprobe- and laser ablation mass spectrometric analyses of polished whole particle mounts confirmed differences in gold/silver content/distribution and trace metal content between particles from epi- and mesothermal sources, respectively. On particles from all sites nano- and micro-particulate gold is associated with polymorphic layers. These are composed of microbial cells, extracellular polymeric substances (EPS) and clay-sized minerals. Multivariate statistical analyses shows a significant difference between biofilm communities from epi- vs. mesothermally derived particles, which is linked to the chemical composition of the primary gold. While a number of key-species capable of gold transformation, e.g., Cupriavidus sp., Geobacter sp. and Rhodoferax sp., were detected on particles from both sources, higher numbers of organisms with the potential for gold solubilization, precipitation and detoxification were associated with particles from the epithermal sources. A range of species involved in gold transformation, i.e., Arthrobacter spp., Delftia sp., Shewanella sp., and Stenotrophomonas spp., were detected only on epithermally derived placer gold. This indicates the communities are sensitive to differences in gold/silver and possibly trace metal-cycling, resulting from differences in their content, distribution and mobilization behaviour in epi- vs. mesothermally derived particles. Ultimately, this study shows that the chemical composition of the primary deposit strongly influences the biogeochemical transformation of placer gold and the composition of associated biofilms, whereas physical transformations appear to be largely unaffected. 相似文献
3.
The first occurrence of platinum group minerals (PGM) in a chromite deposit in the Eastern Desert, Egypt 总被引：1，自引：0，他引：1
M. A. Elhaddad 《Mineralium Deposita》1996,31(5):439-445
The platinum-group mineralogy (PGM) of the chromitite from Gebel Lawi, in the southeastern desert has been investigated.
The most abundant base metal sulfides (BMS) associated with the Lawi chromite are pentlandite, millerite and heazlewoodite.
The major platinum-group minerals identified were as follows: laurite (IrOsRu)S2, osmian iridium (OsIr), hollingworthite (RhAsS),
tellurian arsenopalladinite (PdTeSbAs), potarite (PdHg) besides cuprian palladian gold (CuPdAu), a Pd-Sb-Hg and HgTe phases.
Laurite and osmian iridium occur preferentially in chromite. Os-Ir commonly forms composite PGM with laurite. Hollingworthite
and tellurian arsenopalladinite are included within serpentine and, close to the base-metal sulfides, the cuprian palladian
gold shares boundaries with chromite. Potarite together with the Pd-Sb-Hg and HgTe phases are embedded in serpentine. Palladium
is the most abundant PGE in the Gebel Lawi chromite.
A paragenetic sequence of PGM formation is described. Textural evidence indicates that Os-, Ir- and Ru-bearing PGM formed
early and were followed by Rh- and Pd-bearing PGM. The concentration of all five PGE could be magmatic, but much of the PGE
mineralogy except for laurite and osmian iridium in the center of chromite grains, has been modified by subsequent processes.
At later stages, the environment became Te-, Sb-, As- and Hg-rich, which finally led to the formation of low-temperature alteration
minerals.
Received: 24 April 1995 / Accepted: 28 March 1996 相似文献
4.
Platinum group minerals (PGM) are rather widespread as admixture in gold placer deposits in Tuva. The present paper reports new data on PGM in the Kundus gold placer confined to the Kaakhem ophiolite belt. The minerals are mainly represented by solid solutions of the Os-Ir-Ru system. They make up rims of sulfoarsenides, sulfides, and arsenides of the platinum group elements (PGE) developed after primary minerals. PGMs of this placer always contain traces of Pd (0.33–1.58 wt %), Cu (0.29–0.50 wt %), and As (0.03–2.17 wt %), as well as Ni and Sb (within the detection limit). Typomorphic features of minerals along with the set of main elements and isomorphic trace-elements in the major and secondary mineral species, suggest that sources for the studied placer was represented by the Alpine-type ultramafics and associated chromitites. We cannot also rule out that PGM mineralization was influenced later intrusions that promoted the formation of rims of sulfoarsenides, sulfides, and arsenides of PGE. The PGM rims are marked by the S and As isomorphism, which characterizes the composition of mixtures rather than independent mineral types (end members of isomorphic series). In one case, minerals are represented by the isomorphous mixture of sulfoarsenides with a limited role of sulfides; in another case, by arsenides with a limited role of sulfoarsenides. 相似文献
5.
新疆金矿主要成因类型 总被引：6，自引：1，他引：6
作者根据目前金矿大多数成因分类方案原则,即采用以成矿作用作为一级分类原则将新疆已知金矿床(点)划分为岩浆热液型、变质热液型、火山热液型和外生砂金等四种成因类型.又依据含金建造、成矿部位以及外地质营力把变质热液型、火山热液型和砂金进一步各分为两个亚型.新疆热液型金矿的成矿时代以华力西晚期为主. 相似文献
6.
Summary ?We report, for the first time, the occurrence of five palladium-rich, one palladium bearing and two gold-silver minerals
from podiform chromitites in the Eastern Alps. Minerals identified include braggite, keithconnite, stibiopalladinite, potarite,
mertieite II, Pd-bearing Pt-Fe alloy, native gold and Ag-Au alloy. They occur in heavy mineral concentrates produced from
two massive podiform chromitite samples (unaltered and highly altered) of the Kraubath ultramafic massif, Styria, Austria.
Distribution patterns of platinum-group elements (PGE) in these chromitites show considerable differences in the behaviour
of the less refractory PGE (PPGE-group: Rh, Pt, Pd) compared to the refractory PGE (IPGE-group: Os, Ir, Ru). PPGE are more
enriched in chromitite showing pronounced alteration features. The unaltered chromitite displays a negatively sloped chondrite-normalised
PGE pattern similar to typical ophiolitic-podiform chromitite.
Except for the Pd- and Au-Ag minerals that are generally rare in ophiolites, about 20 other platinum-group minerals (PGM)
have been discovered. They include PGE-sulphides (laurite, erlichmanite, kashinite, bowieite, cuproiridsite, cuprorhodsite,
unnamed Ir-rich variety of ferrorhodsite, unnamed Ni-Fe-Cu-Rh- and Ni-Fe-Cu-Ir-Rh monosulphides), PGE alloys (Pt-Fe, Ir-Os,
Os-Ir and Ru-Os-Ir), PGE-sulpharsenides (irarsite, hollingworthite, platarsite, ruarsite and a number of intermediate species),
sperrylite and a Ru-rich oxide (?). Three PGM assemblages have been recognised and attributed to different processes ranging
from magmatic to hydrothermal and weathering-related.
Pd-rich minerals are characteristic of both chromitite types, although their chemistry and relative proportions vary considerably.
Keithconnite, braggite and Pd-bearing ferroan platinum, together with a number of PGE-sulphides (mainly laurite-erlichmanite)
and alloys, are typical only of the unaltered podiform chromitite (assemblage I). Euhedral mono- and polyphase PGM grains
in the submicron to 100 μm range show features of primary magmatic assemblages. The diversity of PGM in these assemblages
is unusual for ophiolitic environments. In assemblage II, laurite-erlichmanite is intergrown with and overgrown by PGE-sulpharsenides;
other minerals of assemblage I are missing. Potarite, stibiopalladinite, mertieite II, native gold and Ag-Au alloys, as well
as PGE-sulpharsenides, sperrylite and base metal arsenides and sulphides are characteristic for the highly altered chromitite
(assemblage III). They occur either interstitial to chromite in association with metamorphic silicates, in chromite rims or
along cracks, and are thus interpreted as having formed by remobilization of PGE by hydrothermal processes during polyphase
regional metamorphism.
Received August 3, 2000;/revised version accepted December 28, 2000 相似文献
7.
Compositional variations and morphological evolution in platinum beach placers, southern New Zealand
Morphologies of placer platinum group minerals (PGM) are more variable and resistant to modification during transport than placer gold grains. This study documents morphological evolution of PGM placer grains during up to 120 km of transport in beach placers after river transport from inferred sources up to 200 km inland. PGM morphological changes are calibrated with changes in morphology of associated placer gold. Most of the PGM are Pt-Fe alloy and have been fed into the beach placer system from a large river at the western end of the beaches on the south coast of New Zealand. The incoming fluvial PGM suite includes Os, Ir and Ru alloys which may have been derived from distal ophiolitic sources. More proximal sources have Ural-Alaskan affinities and these contributed cooperite and braggite, or sperrylite, locally, as well as Pt-Fe alloy grains. Some PGM may have been recycled through Cretaceous-Quaternary fluvial sediments before entering the modern placer system. Recycled placer PGM grains have also been derived from elevated Quaternary beaches near the coastline. PGM grains entering beach placers have rough surfaces, with remnants of crystal faces, and these evolve to smooth flakes with progressive long-shore transport. PGM flakes have slightly thickened rims caused by impacts by saltating sand on windy beaches, and the most distal beach placers contain flakes with incipient toroidal shapes. These PGM incipient toroids are poorly developed compared to accompanying well-formed toroidal gold that has developed in nearly all beach placers, including those on elevated Quaternary beaches. Typical PGM and gold placer grain size decreases with increasing distance of transport, from fluvial grain size of 400–1,000 to ～200 microns on the most distal beaches, accompanied by eastward loss of equant PGM grains and associated increase in proportion of flakes. Although net transport distance is ～120 km in the beach placer complex, frequent aeolian transport of grains from beach to dunes and subsequent recycling by storm surges substantially increased total transport distance in a dynamic windy tectonic environment. 相似文献
8.
双口山金- 银- 铅矿床地处柴北缘西段,赋存在滩间山变基性- 超基性变火山岩中。矿体由金矿体和银铅矿体组成,成矿作用与热液活动密切相关。本文通过对双口山含金矿体赋矿围岩及含金石英脉进行LA- ICP- MS锆石U- Pb年代学分析和研究。结果表明,赋矿围岩形成时代为443±2. 9Ma,与区域滩间山群火山岩形成年代一致(440~490Ma)。含金石英脉热液锆石U- Pb年代为402. 8±4. 2Ma,与区域金矿床成矿年龄以及韧性剪切带年龄相接近(~400Ma),代表了金矿体热液作用及成矿时代。结合地质特征及前人研究,表明双口山金银铅矿床是柴北缘造山带在不同造山带演化阶段,由不同成矿作用,在不同时期,相互叠加形成的复合型多金属矿床。金矿体具有典型造山型金矿床特征的变质热液型金矿,其成因主要与造山运动过程中的变质和变形作用有关, 成矿物质和流体来源于绿片岩相的滩间山群变基性- 超基性变火山岩。银铅矿体为岩浆热液型,成矿与后碰撞造山作用伸展- 构造转换有关的岩浆作用有关,成矿物质和流体来源于晚泥盆世深部含矿岩浆作用。 相似文献
9.
运用矿床的成矿系列理论,以构造岩浆演化为基础,对吉中- 延边成矿带与燕山期岩浆作用有关的矿床成矿规律进行了分析总结。研究表明,受古太平洋板块俯冲方向、速度的制约,吉中—延边地区燕山期构造岩浆活动复杂,总体上可分为5次成岩成矿事件：① 晚三叠世初基性超基性岩侵入,形成红旗岭铜镍矿床等岩浆型矿床;② 晚三叠世—早侏罗世初,吉中地区高钾钙碱性岩浆活动,形成兰家金矿床等岩浆热液型矿床,延边地区中低钾钙碱性—高钾钙碱性岩浆活动,形成前山金矿床等火山- 潜火山岩型矿床;③ 早侏罗世末—中侏罗世初,富铝酸性岩浆活动,形成大黑山钼矿床等斑岩型钼矿床;④ 中侏罗世末—晚侏罗世初,研究区以抬升剥蚀为主,成岩成矿作用较弱;⑤ 晚侏罗世末—早白垩世,吉中地区高钾钙碱性岩浆活动,形成二道甸子金矿床等岩浆热液型矿床,延边地区中低钾钙碱性—高钾钙碱性岩浆活动,形成小西南岔金铜矿床等火山- 斑岩型矿床。在建立吉中—延边地区与燕山期岩浆作用有关的矿床成矿系列的基础上,进一步划分为6个矿床成矿亚系列,各亚系列在时间、空间上既有联系,又有区别,显示了成矿作用的复杂性。 相似文献
10.
A. G. Mochalov 《Geology of Ore Deposits》2013,55(3):145-161
A genetic model has been developed for platinum group minerals (PGM) hosted in plutonic gabbro-pyroxenite-dunite (GPD) complexes of the Koryak Highland. The following mineralogical-geochemical and genetic PGM types have been distinguished: (1) magmatic platinum (Pt), (2) magmatic-fluid-metasomatic platinum (Pt) and osmium-platinum (Pt > Os), (3) fluid-metamorphic iridium-platinum (Pt > Ir), and (4) hydrothermal metasomatic platinum-copper (Pt-Cu). PGM of the magmatic Pt type were formed under conditions of monocyclic petrogenesis of Cr-spinel-olivine and olivine-clinopyroxene cumulates as products of picritic magma fractionation in the conduit chamber. The magmatic-fluid-metasomatic platinum Pt and osmium-platinum Pt > Os types were formed by interaction of these early cumulates with magma. The abundance of these types is proportional to injections of picritic magma into the conduit chamber. PGM of the fluid-metamorphic iridium-platinum Pt > Ir type accumulated as a result of synmagmatic recrystallization of GPD cumulates. Their development depends on (1) mono- or polycyclic GPD cumulative complex and (2) the degree of GPD cumulate recrystallization from partial to complete and the degree of transformation of PGM pertaining to the magmatic and magmatic-fluid-metasomatic Pt types. The monocyclic GPD complexes are low-prospective in respect to magmatic Pt deposit formation. The polycyclic GPD complexes differ in their prospectivity from ore occurrences to unique magmatic-fluid-metasomatic Pt and Pt > Os deposits, as well as deposits of the fluid-metamorphic Pt > Ir type. The genetic types of PGM accumulation imply a multifactor system of ore-forming processes with the participation of platinum-group elements (PGE) in GPD complexes. The genetically different PGM accumulations in GPD complexes should be regarded as self-dependent geological objects of local forecasting. In this connection, it is necessary to renew mineralogical and geochemical criteria for prospecting and exploration of PGM genetic types in GPD complexes as well as their mining conditions. 相似文献
11.
根据 2 0世纪 90年代铂族金属矿床勘查的新发现 ,提出铂族金属矿床成因分类 ,探讨中国铂族金属找矿方向 ,提出“以绿找铂”、“以黄找铂”和“以黑找铂”的找矿原则 ,即在蛇绿混杂岩或基性—超基性岩分布区寻找基性—超基性岩浆岩型、岩浆热液型铂族金属矿以及与之有关的砂铂矿床 ,在金矿田中寻找伴生铂族金属矿床 ,在黑色页岩分布区寻找黑色页岩型铂族金属矿床。 相似文献
12.
金川铜镍硫化物矿床是我国最主要的铂族元素(PGE)资源产地,其矿石受热液蚀变作用影响明显,并产出多种铂族矿物(PGM)。岩浆演化和热液蚀变过程中PGE的迁移富集机制和PGM的成因,一直是研究PGE地球化学行为非常关注的问题。本文对金川铜镍硫化物矿床中PGM的研究发现,其主要类型包括含PGE的硫砷化物(硫砷铱矿)和砷化物(砷铂矿),Pd的铋化物、碲化物和硒化物,以及少量其他铂族矿物。其中,硫砷铱矿可包裹于各种贱金属硫化物(镍黄铁矿、磁黄铁矿和黄铜矿)中,表明硫砷铱矿可能结晶于早期的含As硫化物熔体,随后被包裹于硫化物熔体冷凝分异产生的单硫化物固溶体(MSS)和中间硫化物固溶体(ISS)中。硫化物熔体中的As可能主要通过地壳混染作用加入幔源岩浆。大量铋钯矿(PdBi)呈微细乳滴状包裹于黄铜矿中,为晚期ISS冷凝形成黄铜矿过程中出溶的产物。少量铋钯矿(PdBi_2)呈不规则状充填于矿物裂隙,与次生磁铁矿脉紧密共生,并随矿石的蚀变程度增加,铋钯矿的化学成分由PdBi逐渐向PdBi_2转变,表明这部分铋钯矿为后期热液蚀变产物。铋碲钯矿和钯的硒化物则主要产出于镍黄铁矿裂隙且与次生磁铁矿紧密共生,指示明显的热液成因。钯的硒化物的出现表明,岩浆期后酸性、高盐度、高氧逸度的富Cl~-流体对金川铜镍硫化物矿床中Pd的迁移和富集起到了关键控制作用。 相似文献
13.
华北陆块北缘中段金矿床分布较多 ,产出较为集中 ,也是我国重要的黄金生产基地。本区是我国地质历史演化最久 ,又经历了多期、多阶段的构造 -岩浆活动的叠加 ,因而金矿床的形成具有多期性、多样性、继承性和新生性等特点。本区金矿床主要产在绿岩带构造 -岩浆活动的有利部位 ,统称绿岩带型金矿床 ,可分为同构造晚期初生型金矿床和构造期后再生型热液金矿床两类 ,又可细分为若干亚类 ,其中再生型热液金矿床分布较广 ,规模较大 ,具有较大找矿潜力。由于区内发育多期、多阶段的成矿构造 -岩浆活动 ,因而在一个金矿床密集区内 ,有时在不同的构造部位 ,分别产出初生型和再生型热液金矿床 ,这是指导找矿的重要地质依据 相似文献
14.
The mineral assemblage and the sedimentological characteristics of the “Donauplatin” (Danubian fluvial placer containing platinum-group elements (PGE) and gold (Au)) are described for the first time in connection with upstream reference placer deposits near the potential source area in tributaries of the River Danube/Donau. Granulometric and morphometric data have been obtained using the CCD-based CAMSIZER technique. The platinum-group minerals (PGM; iridium, osmium, unknown iridium-osmium-sulfide, ruthenium-osmium-iridium alloys, platinum-iron alloys, iridium-bearing platinum, sperrylite) have been derived from ultramafic magmatic rocks, probably belonging to the ophiolitic series in the Tepla Barrandian unit of the Bohemian Massif. The Au-Pd-Cu compounds in the placer originated from dynamo-metamorphogenic processes in a sulfur-deficient environment at the SW edge of the Bavarian Basement. Gold in the “Donauplatin” has been reworked from a “secondary” or intermediate repository of lateritic gold (Boddington-type). Its primary source is supposed to be of orogenic origin. Provenance analyses of the associated non-heavy minerals point to high-pressure metamorphic rocks, igneous rocks (monazite) and high-temperature metamorphic rocks (750° to 850°C, zircon morphology). Garnet compositions indicate that meta(ultra)basic igneous rocks, calc-silicate rocks and skarns prevailed over paragneisses in the provenance area. Extraterrestrial processes creating the well-known Ries impact crater in the environs of Nördlingen during the Miocene have a minor share in the PGE budget by delivering molybdenum-ruthenium-osmium-iridium alloys and iridium solid-solution series (s.s.s.) minerals. Judging by the heavy mineral suites, Saxothuringian source rocks of the NE Bavarian Basement connected with the Donau River via the Naab River drainage system have not contributed to the element budget of the “Donauplatin” under study. Stream sediments which have been derived from this provenance area are characterized by low-temperature (LT) crystalline rocks and a considerable proportion of pegmatitic and metabauxitic material lacking in the Holocene sediments of the “Donauplatin”. 相似文献
15.
M. A. E. Huminicki P. J. Sylvester R. Lastra L. J. Cabri D. Evans-Lamswood D. H. C. Wilton 《Mineralogy and Petrology》2008,92(1-2):129-164
Summary This study reports the first documented occurrence of platinum group-minerals (PGM) in the vicinity of the Voisey’s Bay magmatic
sulfide ore deposit. The PGM are present in a sulfide poor, hornblende gabbro dyke in the Southeast Extension Zone of the
massive sulfide Ovoid deposit. The dyke has somewhat elevated concentrations of platinum-group elements (PGE) and gold (up
to 1.95 g/t Pt, 1.41 g/t Pd, and 6.59 g/t Au), as well as Cu, Pb, Ag, Sn, Te, Bi and Sb. The PGM formed by magmatic processes
and were little disturbed by subsequent infiltration of an externally-supplied hydrothermal fluid. To date, no similar PGM
occurrences have been discovered in the Ovoid deposit itself.
Whole rock REE patterns indicate that the dyke is geochemically related to the main conduit troctolites, which carry the bulk
of the massive sulfide mineralization at Voisey’s Bay. The PGE mineralization is Pt- and Pd-rich, where the Pt and Pd occur
predominantly as discrete PGM with minor Pd in solid solution in galena (average=1.8 ppm) and pentlandite (average=2 ppm).
The discrete PGM are predominantly hosted by disseminated base-metal sulfides (bornite, chalcopyrite, and galena) (56 vol%)
and are associated with other precious metal minerals (13 vol%) with only ∼3 vol% of the PGM hosted by silicate minerals.
In whole rock samples, the PPGE (Pt, Pd, and Rh) correlate with abundances of chalcopyrite, bornite, galena, and other precious
metal minerals (PMM), whereas the IPGE (Ir, Ru, and Rh) correlate with pyrrhotite and pentlandite. There are no correlations
of the PGE with chlorine. Lead isotope compositions of galena associated with the PGE mineralization in the Southeast Extension
Zone are broadly similar to those for galena in the Ovoid. The lead isotope compositions are much different from those in
the Voisey’s Bay Syenite, which is a potential external hydrothermal fluid source.
The observed Cu-rich, Pb-rich sulfide compositions and associated Pt-Pd-Au-Ag-Sn-Te-Bi-Sb assemblage in the dyke can be produced
magmatically as late ISS differentiates (e.g., Prichard et al., 2004). Melting temperatures of the PGM are also consistent with a magmatic origin. Following crystallization of PGM
from magmatic sulfide, an external REE-enriched hydrothermal fluid was introduced to the system, producing secondary amphibole
and locally remobilizing the Pb and Sn from the sulfides hosting the PGM.
Author’s address: M. A. E. Huminicki, Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, NL, Canada A1B 3X5 相似文献
16.
17.
达拉松金矿床位于俄罗斯东亚地区,是世界驰名的超大型金矿床之一。矿床形成具有经历过多个大地构造成矿阶段、多种成因成矿和多种金来源的特征。主成矿作用是中低温热液作用,成矿热液和成矿驱动力与中生代地洼阶段构造-岩浆活化有密切关系。成矿热液中的金来自地槽阶段海西期花岗岩内的金再造和地洼阶段的深部金源。热液成矿后矿区地壳继续隆起,导致风化剥蚀作用强烈发育,在达拉松河谷阶地内形成沉积砂金矿化。因而,该矿床的形成类似于层控金矿床原理,只是矿源层在该区应为矿源岩体。矿区内既有内生金成矿富集,又有外生砂金成矿富集,共同组成一个超大型金矿床。据此将该矿床列为多因复成金矿床类型。 相似文献
18.
将内蒙古已知金矿划分为5大类型20个矿床亚类:即重熔岩浆热液金矿、变质热液金矿、沉积变质热液金矿、火山-次火山热液金矿、砂金矿.对各类型金矿床的地质成因特征进行了初步探讨. 相似文献
19.
将内蒙古已知金矿划分为5大类型20个矿床亚类：即重熔岩浆热液金矿、变质热液金矿、沉积变质热液金矿、火山-次火山热液金矿、砂金矿。对各类型金矿床的地质成因特征进行了初步探讨。 相似文献
20.
Hartwig Frimmel 《地学学报》1997,9(4):192-197
The Witwatersrand 'basin' is the largest known gold province in the world. The gold deposits have been worked for moren than 100 years but there is still controversy about the ore forming process. Detailed petrographic studies often reveal that the gold is late in the paragenetic sequence, which has led many researchers to propose a hydrothermal origin for the gold. However, observations, such as the occurrence of rounded, disc-like gold particles next to irregularly shaped or idiomorphic secondary gold particles in the same sample, suggest an initial detrital gold source within the Witwatersrand strata. Mineral chemical and isotopic data, together with SEM cathodoluminescence imaging and fluid inclusion studies, provide evidence for small-scale variations in the fluid chemistry – a requirement for the short-range mobilization of the gold. The existing data and observations on the Witwatersrand rocks support a model of hydrothermally altered, metamorphosed placer deposits, with at least two subsequent gold mobilization events: hydrothermal infiltration in early Transvaal time (2.6–2.5 Ga) and during the 2.020 Ga Vredefort impact event. 相似文献