新疆哈密卡拉塔格块状硫化物矿床金银赋存状态研究

新疆哈密红海黄土坡VMS矿床位于东天山卡拉塔格隆起带,是卡拉塔格矿集区内新发现的块状硫化物矿床。矿体产于卡拉塔格隆起带核部火山沉积岩建造中,具有典型的VMS型矿床“上层下脉”二元结构特征。该矿床中含金硫化物矿石主要有块状黄铁矿黄铜矿、块状黄铁矿黄铜矿闪锌矿、块状黄铁矿闪锌矿黄铜矿和块状闪锌矿。文中在对各类含金硫化物矿石进行详细的矿相学研究基础上,结合扫描电子显微镜与能谱仪联用技术(SEM/EDS),对硫化物样品中金、银的赋存状态进行研究。结果表明,4种块状硫化物中的主要矿物形成于多个期次,主要包括VMS成矿期(黄铁矿阶段、闪锌矿黄铜矿黝铜矿方铅矿阶段、石英重晶石阶段)、热液叠加期(石英黄铁矿黄铜矿闪锌矿方铅矿阶段)和表生期(铜蓝纤铁矿阶段)。矿区首次发现4颗金银金属互化物(银金矿、碲银矿),其较大的化学成分差异指示了热液环境由中酸性中性转变为更有利于Au、Ag迁移沉淀的偏碱性。后期的偏碱性热液对VMS成矿期形成矿物产生了交代作用,使得Au、Ag活化再富集。由于后期热液叠加改造,红海VMS型矿床中Au、Ag不仅赋存于VMS成矿期后期中低温闪锌矿黄铜矿阶段,也赋存于VMS成矿期早期中高温黄铁矿阶段,并贯穿整个热液叠加期。各含金矿物组合中除4颗金银金属互化物外Au多呈显微不可见状态,推测Au、Ag主要以原子或离子形式赋存于矿物晶格中或矿物空位处。     

Gold Enrichment in the Supergene Zone of a Southern Urals Pyrite Deposit,Russia

The Gay deposit, situated in the Orenburg region, is identified with one of Russia's principal occurrences of pyrite (pyrite deposits are an important source of Russia's gold). It belongs to the west subzone of the Magnitogorsk synclinorium and occurs in Devonian rhyolite-basaltic volcanic rocks. The deposit comprises five large pyrite-chalcopyrite, pyrite-chalcopyrite- sphalerite, and pyrite orebodies. The supergene zone extends to 120-240 m below surface and consists of the following three subhorizontal zones (from bottom to top): the secondary sulfide enrichment, the leaching, and the oxidation zone (where ores are enriched in gold).

There are two levels of secondary gold enrichment in the weathering profile. The lower level, located in the leaching zone, corresponds with the level of water table fluctuations. The rich, flat-lying horizon (1.5-10.0 m) is composed of bedded, friable native sulfur-quartz ores; it contains 19.0-52.2 ppm Au and up to 389 ppm Ag. Native gold and silver halides (chlorargyrite, iodargyrite, and embolite) are the principal precious-metal minerals. Electrum, native silver, acanthite, and uytenbogaardtite constitute the minor ones. The upper level of the enrichment is located in the lower part of gossan. This bonanza is composed of hematite-quartz ochres. Gold concentration is 13.5 to 21.2 ppm. Native gold of high fineness and silver halides apparently are associated here with poorly crystallized iron oxides. The formation of supergene gold enrichments may result partly from residual concentration and partly from mobilization and reprecipitation of the precious metal. Rich horizons form by repeated gold redeposition in accordance with weathering and a gradual erosion surface lowering. The lower bonanza forms at first in the process of oxidation involving pyrite and native sulfur. Gold may be transported by complexes with metastable sulfur oxy-anions: sulfites, thiosulfates, or polythionates. The upper enriched horizon forms in the course of further evolution of the weathering profile in the stage of hematite recrystallizaiton and its transformation into goethite.     

Mineralogical evolution of the Las Cruces gossan cap (Iberian Pyrite Belt): From subaerial to underground conditions

The Las Cruces VMS deposit is located at the eastern corner of the Iberian Pyrite Belt (SW Spain) and is overlain by the Neogene–Quaternary sediments of the Guadalquivir foreland Basin. The deposit is currently exploited from an open pit by Cobre Las Cruces S.A., being the supergene Cu-enriched zone the present mined resource. The Las Cruces orebody is composed of a polymetallic massive sulfide orebody, a Cu-rich stockwork and an overlying supergene profile that includes a Cu-rich secondary ore (initial reserves of 17.6 Mt @ 6.2% Cu) and a gossan cap (initial reserves of 3.6 Mt @ 3.3% Pb, 2.5 g/t Au, and 56.3 g/t Ag).The mineralogy of the Las Cruces weathering profile has been studied in this work. Textural relationships, mineral chemistry, deposition order of the minerals and genesis of the Las Cruces gossan are described and discussed in detail. A complex mineral assemblage composed by the following minerals has been determined: carbonates such as siderite, calcite and cerussite; Fe-sulfides including pyrite, marcasite, greigite and pyrrhotite; Pb–Sb sulfides and sulfosalts like galena, stibnite, fulöppite, plagionite, boulangerite, plumosite, and the jordanite–geocronite series, Ag–Hg–Sb sulfides and sulfosalts including miargyrite, pyrargyrite, sternbergite, acanthite, freibergite, cinnabar, Ag–Au–Hg amalgams; and Bi–Pb–Bi sulfides and sulfosalts such as bismuthinite, galenobismutite, others unidentified Bi–Pb-sulfosalts, native Bi and unidentified Fe–Pb–Sb-sulfosalts. Remains of the former oxidized assemblage appear as relicts comprised of hematite and goethite.Combining paragenetic information, textures and mineral chemistry it has been possible to derive a sequence of events for the Las Cruces gossan generation and subsequent evolution. In that sense, the small amount of Fe-oxyhydroxides and their relict textures replaced by carbonates and sulfides suggest that the gossan was generated under changing physico-chemical conditions. It is proposed that the Las Cruces current gossan represents the modified residue of a former gossan mineralization where prolonged weathering led to dissolution and leaching out of highly mobile elements and oxidation of the primary sulfides. Later, the gossan was subject to seawater-gossan interaction and then buried beneath a carbonated-rich cover. The basinal fluids-gossan interaction and the equilibration of fluids with the carbonated sediments brought to the carbonatization and sulfidation of the gossan, and thus to the generation of Fe-carbonates and Pb–Sb-sulfides.The Las Cruces mineral system likely represents a new category within the weathering class of ore deposits.     

吉林东部地区与火山岩-斑岩有关的金(铜银)矿成矿地质特征及其成矿模式

吉林东部地区与火山岩-斑岩有关的金(铜银)矿床可分为浅成低温热液型金(银)矿和浅成中温斑岩。热液型金(铜)矿两个亚类。浅成低温热液型矿床的特征矿物组合为黄铁矿、石英、方解石、冰长石和重晶石,成因上与高钾的钙碱性火山岩。斑岩(137～177Ma)有关,成矿流体属浅成低温氧化流体,在成矿过程中大气降水混入的程度大。浅成中温斑岩,热液型矿床的特征矿物组合为黄铁矿、黄铜矿、磁黄铁矿和石英,成因上与钙碱性火山岩。斑岩(130～140Ma)有关,成矿流体属浅成中温还原流体,在成矿过程中大气降水混入的程度相对较小。由于火山岩,斑岩的来源深度不同,斑岩体在矿床的形成中所起的作用不同,成矿流体的性质不同,造成金矿床的类型不尽相同。     

河南铝土矿矿物成因及其演化序列

[摘 要]豫西铝土矿是我国喀斯特型铝土矿的典型代表。本文选取豫西典型的喀斯特型铝土矿为研究对象,通过XRD 分析、扫描电镜-能谱分析、电子探针分析和差热分析多种手段,探测铝土矿的物质组成及其赋存状态,并且分析其矿物成因,总结矿物演化序列。研究显示,豫西铝土矿的主要矿物成分包括硬水铝石、伊利石、锐钛矿、高岭石、针铁矿、赤铁矿、金红石等。硬水铝石主体为简单结晶成因。伊利石主体为风化过程中产物,部分为后期硬水铝石硅质交代的结果。锐钛矿和硬水铝石同期结晶形成于还原环境下。大部分高岭石形成于陆源期风化阶段,少部分为后期硬水铝石硅化转变形成。针铁矿和赤铁矿形成于两个阶段,第一阶段为成矿前风化作用形成的铁质风化壳;第二阶段为铝土矿成岩晚期出现了一期铁质流体活动形成了大量的赤铁矿和针铁矿。重砂矿物金红石和锆石等主要是母岩风化作用的残留物。豫西铝土矿中矿物形成演化可归纳为如下五个阶段:陆源期、同生期、成矿期、成矿后期和表生期。     

桂西那弱银金矿床矿物组合特征及银和金的赋存状态研究

广西天峨那弱银金矿床以银矿为主,共/伴生金及铅、锌、锑等金属,矿物组合在右江盆地内为首次发现。矿体受那弱背斜及其轴向断层控制,赋矿层位为中三叠统百逢组含钙质浊积岩系。矿石矿物以硫锑铅矿、铁闪锌矿、黄铁矿、毒砂和方铅矿为主;脉石矿物主要有石英、方解石、绢云母等。主要矿石矿物由早到晚的生成顺序为:毒砂→黄铁矿→铁闪锌矿→硫锑铅矿→方铅矿。单矿物化学分析显示硫锑铅矿含Ag最高,其次为闪锌矿;黄铁矿含Au相对较高。EPMA测试结果表明Ag于方铅矿中含量最高,其次为硫锑铅矿;主要矿石矿物中毒砂含Au相对较高,其余矿物中Au含量均偏低。因矿石中的铅矿物主要为硫锑铅矿,可以认为那弱银金矿床的Ag主要赋存于硫锑铅矿中,Au主要赋存于毒砂与黄铁矿中,二者均以显微-次显微状态赋存于载体矿物中。根据矿物组合及其相互交代、切割关系等特征,将矿床划分为2个成矿期共4个成矿阶段。其中,第一成矿期为金的成矿期,矿物组合为黄铁矿和毒砂,由于后期成矿作用的叠加,仅保留一个成矿阶段;第二成矿期为银铅锌成矿期,矿物组合为方铅矿-闪锌矿-硫锑铅矿;包含第二至第四共3个完整的成矿阶段。该矿床Ag、Au共生是不同期次成矿作用叠加的结果。     

湖北银洞沟银矿床地质特征与成因类型

湖北银洞沟矿床是中国为数不多的较为典型的大型银矿床。文中系统总结了该矿床的地质特征,初步提出了矿床的成因类型。研究结果表明:银洞沟矿床产于秦岭造山带东南部武当群变质火山岩中,矿体受韧性剪切带控制,矿石类型主要为石英脉型和少量蚀变岩型,围岩蚀变矿物组合主要为石英、铁白云石、白云母、钠长石、绿泥石、黄铁矿等,成矿流体特征为低盐度、低密度、富含CO2±CH4±N2的水溶液,矿床上部为低品位银金矿体,中部为高品位银金矿体和少量铅锌矿体,深部银品位降低,金品位增高,同时出现较厚大铅锌矿体。其地质特征与典型的造山型矿床一致,表明其为一造山型银矿床,矿床矿化分带符合造山型矿床成矿模式——地壳连续模型,因此应该充分重视寻找矿山深部金、铅、锌、铜、钼等接替资源。     

福建尤溪肖板金矿床金的赋存状态及金矿物特征

肖板金矿床属受构造控制的中低温岩浆热液矿床,矿化类型为构造蚀变岩型。金多呈独立金矿物形式出现,少许呈分散状;金矿物以自然金为主,平均成色９３０,有少量银金矿和碲金矿。金矿物以包体金、裂隙金、连生金和粒间金等形式嵌布于黄铁矿、黄铜矿、石英、方铅矿及方解石等主要载金矿物中,且石英、方解石中较金属硫化物中占优势。金矿物形态各异,粒度以中细粒为主。     

Linear weathering crusts in the upper Amur region

The upper Amur region comprises weathering crusts (waste mantle developed at copper-nickel sulfide deposits included), which appreciably hamper the prospecting for such deposits. In order to develop their prospecting criteria, the composition of linear weathering crusts above a nickeliferous cortlandite dike and barren pyroxenite dike, as well as in the fracture zone above metamorphic rocks, was investigated. The chemical composition of material in the weathering crust and the mineral composition of newly formed clay fractions and heavy concentrate were determined. It was established that weathering crust in the nickeliferous cortlandite dike is characterized by the prevalence of fine jarosite fraction with crystobalite admixture. The heavy concentrate samples contain jarosite along with a small amount of relict sulfides (pyrite and galena) and native gold. These criteria can be used in the prospecting for copper-nickel sulfide mineralization in the upper Amur region and other similar regions.     

北山地区金矿床金的赋存状态和金矿物特征

甘肃北山地区金矿床主要有岩浆热液型金矿床和与韧性剪切带有关的金矿床,矿化类型为石英脉型和蚀变岩型。金多呈独立金矿物形式出现,少放许呈分散状;金矿物以银金矿为主,次为自然金,平均成色７７２;金矿物以粒间金、裂隙金、连生金、连生金和包体金等形成嵌布于石英、黄铁矿、方铅矿及闪锌矿等主要载物较为发育。金矿物特征反映出本区金矿床的成矿物质主要来源于变质岩,华力西－印支期中酸性岩浆活动是主要的动力源。     

The origin of Ag–Au–S–Se minerals in adularia-sericite epithermal deposits: constraints from the Broken Hills deposit, Hauraki Goldfield, New Zealand

The 7.1 Ma Broken Hills adularia-sericite Au–Ag deposit is currently the only producing rhyolite-hosted epithermal deposit in the Hauraki Goldfield of New Zealand. The opaque minerals include pyrite, electrum, acanthite (Ag₂S), sphalerite, and galena, which are common in other adularia-sericite epithermal deposits in the Hauraki Goldfield and elsewhere worldwide. Broken Hills ores also contain the less common minerals aguilarite (Ag₄SeS), naumannite (Ag₂Se), petrovskaite (AuAgS), uytenbogaardtite (Ag₃AuS₂), fischesserite (Ag₃AuSe₂), an unnamed silver chloride (Ag₂Cl), and unnamed Ag?±?Au minerals. Uytenbogaardtite and petrovskaite occur with high-fineness electrum. Broken Hills is the only deposit in the Hauraki Goldfield where uytenbogaardtite and petrovskaite have been identified, and these phases appear to have formed predominantly from unmixing of a precursor high-temperature phase under hypogene conditions. Supergene minerals include covellite, chalcocite, Au-rich electrum, barite, and a variety of iron oxyhydroxide minerals. Uytenbogaardtite can form under supergene and hypogene conditions, and textural relationships between uytenbogaardtite and associated high-fineness electrum may be similar in both conditions. Distinguishing the likely environment of formation rests principally on identification of other supergene minerals and documenting their relationships with uytenbogaardtite. The presence of aguilarite, naumannite, petrovskaite, and fischesserite at Broken Hills reflects a Se-rich mineral assemblage. In the Hauraki Goldfield and the western Great Basin, USA, Se-rich minerals are more abundant in provinces that are characterized by bimodal rhyolite–andesite volcanism, but in other epithermal provinces worldwide, the controls on the occurrences of Se-bearing minerals remain poorly constrained, in spite of the unusually high grades associated with many Se-rich epithermal deposits.     

Early weathering of palladium gold under lateritic conditions,Maquiné Mine,Minas Gerais,Brazil

Since the 80's, studies have shown that Au is mobile in supergene lateritic surficial conditions. They are based either on petrological, thermodynamic studies, or experimental works. In contrast, few studies have been done on the mobility of the Pt group elements (PGE). Moreover, at the present time, no study has addressed the differential mobility of Au, Ag and Pd from natural alloys in the supergene environment. The aim of this study is to understand the supergene behavior, in lateritic conditions, of Au–Ag–Pd alloys of the Au ore locally called Jacutinga at the Maquiné Mine, Iron Quadrangle, Minas Gerais state, Brazil.The field work shows that the host rock is a “Lake Superior type” banded iron formation (BIF) and that the Au mineralization originates from sulfide-barren hydrothermal processes. Primary Ag–Pd-bearing Au has developed as xenomorphous particles between hematite and quartz grains. The petrological study indicates that the most weathered primary Au particles with rounded shapes and pitted surfaces were found, under the duricrust, within the upper friable saprolite. This layer, however is not the most weathered part of the lateritic mantle, but it is where the quartz dissolution resulting porosity is the most developed. The distribution of Au contents in the weathered rocks are controlled by the initial hydrothermal primary pattern. No physical dispersion has been found. Most of the particles are residual and very weakly weathered. This characterizes early stages of Au particle weathering in agreement with the relatively low weathering gradient of the host itabiritic formations that leads essentially to the development of isostructural saprolite lateritic mantle. Limited dissolution of primary Au particles issued from the friable saprolite induces Pd–Ag depleted rims compared to primary Au particle Pd–Ag contents.In addition, limited very short distance in situ dissolution/reprecipitation processes have been found at depth within the primary mineralization, as illustrated by tiny supergene, almost pure, Au particles. The supergene mobility order Pd>Ag>Au as reflecting early weathering stages of Au–Ag–Pd alloys under lateritic conditions is proposed.     

Alteration and mineralization styles of the orogenic disseminated Zhenyuan gold deposit,southeastern Tibet: Contrast with carlin gold deposit

Orogenic disseminated and Carlin gold deposits share much similarity in alteration and mineralization.The disseminated orogenic Zhenyuan Au deposit along the Ailaoshan shear zone,southeastern Tibet,was selected to clarify their difference.The alteration and mineralization from the different lithologies,including meta-quartz sandstone,carbonaceous slate,meta-(ultra)mafic rock,quartz porphyry and lamprophyre were researched.According to the mineral assemblage and replacement relationship in all types of host rocks,two reactions show general control on gold deposition:(1)replacement of earlier magnetite by pyrite and carbonaceous material;(2)alteration of biotite and phlogopite phenocrysts in quartz porphyry and lamprophyre into dolomite/ankerite and sericite.Despite the lamprophyre is volumetrically minor and much less fractured than other host rocks,it contains a large portion of Au reserve,indicating that the chemically active lithology has played a more important role in gold precipitation compared to structure.LA-ICP-MS analysis shows that Au mainly occurs as invisible gold in fine-grained pyrite disseminated in the host rocks,with Au content reaching to 258.95 ppm.The diagenetic core of pyrite in meta-quartz sandstone enriched in Co,Ni,Mo,Ag and Hg is wrapped by hydrothermal pyrite enriched in Cu,As,Sb,Au,Tl,Pb and Bi.Different host rock lithology has much impact on the alteration and mineralization features.Carbonate and sericite in altered lamprophyre show they have higher Mg than those developed in other of host rocks denoting that the carbonate and sericite incorporated Mg from phlogopite phenocrysts in the primary lamprophyre during alteration.The ore fluid activated the diagenetic pyrite in meta-quartz sandstone leading the hydrothermal pyrite enriched in Cu,Mo,Ag,Sb,Te,Hg,Tl,Pb and Bi,but the hydrothermal pyrite in meta-(ultra)mafic rock is enriched in Co and Ni as the meta-(ultra)mafic rock host rock contain high content of Co and Ni.However,Au and As shear similar range in both types of host rocks indicating that these two elements most likely come from the deep source fluid rather than the host rocks.It was shown in the disseminated orogenic gold deposit that similar hydrothermal alteration with mineral assemblage of carbonate(mainly dolomite and ankerite),sericite,pyrite and arsenopyrite develops in all types of host rocks.This is different from the Nevada Carlin type,in which alteration is mainly dissolution and silicification of carbonate host rock.On the other hand,Au mainly occur as invisible gold in both disseminated orogenic and Carlin gold deposits.     

Genesis of gold and silver sulfides at the Ulakhan deposit (northeastern Russia)

Geology and mineralogy of the Ulakhan Au-Ag epithermal deposit (northeastern Russia, Magadan Region) are considered. A four-stage scheme of mineral formation sequence is proposed. Concentrations of Au and Ag in minerals of early and late parageneses were determined. It has been established that uytenbogaardtite is associated with native gold and hypergenesis stage minerals — goethite, hydrogoethite, or limonite replacing pyrite. The compositions of uytenbogaardtite (Ag₃AuS₂), acanthite (Ag₂S), and native gold were studied. The composition of the Ulakhan uytenbogaardtite is compared with those of Au and Ag sulfides from other deposits. Thermodynamic calculations in the system H₂O–Fe–Au–Ag–S–C–Na–Cl were carried out, which simulate the interaction of native gold and silver with O₂- and CO₂-saturated surface waters (carbonaceous, sulfide-carbonaceous, and chloride-sodium-carbonaceous) in the presence and absence of acanthite and pyrite at 25 °C and 1 bar. In closed pyrite-including systems, native silver and kustelite are replaced by acanthite; electrum, by uytenbogaardtite, acanthite, and pure gold; and native gold with a fineness of 700–900‰, by pure gold and uytenbogaardtite. Under the interaction with surface waters in the presence of Ag₂S and pyrite, Au-Ag alloys form equilibrium assemblages with petrovskaite or uytenbogaardtite and pure gold. The calculation results confirmed that Au and Ag sulfides can form after native gold in systems involving sulfide-carbon dioxide solutions (H₂Saq > 10^–4 m). The modeling results support the possible formation of uytenbogaardtite and petrovskaite with the participation of native gold in the hypergenesis zone of epithermal Au-Ag deposits during the oxidation of Au(Ag)-containing pyrite, acanthite, or other sulfides.     

The geochemistry of gossans associated with Sarcheshmeh porphyry copper deposit,Rafsanjan, Kerman,Iran: Implications for exploration and the environment

The Sarcheshmeh copper deposit is one of the world's largest Oligo-Miocene porphyry copper deposits in a continental arc setting with a well developed supergene sulfide zone, covered mainly by a hematitic gossan. Supergene oxidation and leaching, have developed a chalcocite enrichment blanket averaging 1.99% Cu, more than twice that of hypogene zone (0.89% Cu). The mature gossans overlying the Sarcheshmeh porphyry copper ores contain abundant hematite with variable amounts of goethite and jarosite, whereas immature gossans consist of iron-oxides, malachite, azurite and chrysocolla. In mature gossans, Au, Mo and Ag give significant anomalies much higher than the background concentrations. However, Cu has been leached in mature gossans and gives values close or even less than the normal or crustal content (< 36.7 ppm). Immature gossans are enriched in Cu (160.3 ppm), Zn (826.7 ppm), and Pb (88.6 ppm). Jarosite- and goethite-bearing gossans may have developed over the pyritic shell of most Iranian porphyry copper deposits with pyrite–chalcopyrite ratios greater than 10 and therefore, do not necessarily indicate a promising sulfide-enriched ore (Kader and Ijo). Hematite-bearing gossans overlying nonreactive alteration halos with pyrite–chalcopyrite ratios about 1.5 and quartz stringers have significant supergene sulfide ores (Sarcheshmeh and Miduk). The copper grade in supergene sulfide zone of Sarcheshmeh copper deposit ranges from 0.78% in propylitized rocks to 3.4% in sericitized volcanic rocks, corresponding to the increasing chalcopyrite–pyrite or chalcocite–pyrite ratios from 0.3 to 3, respectively. Immature gossans with dominant malachite and chrysocolla associated with jarosite and goethite give the most weakly developed enrichment zone, as at God-e-Kolvari. The average anomalous values of Au (59.6 ppb), Mo (42.5 ppm) and Ag (2.6 ppm) in mature gossans associated with the Sarcheshmeh copper mine may be a criterion that provides a significant exploration target for regional metallogenic blind porphyry ore districts in central Iranian volcano–plutonic continental arc settings. Drilling for new porphyry ores should be targeted where hematitic gossans are well developed. The ongoing gossan formation may result in natural acidic rock drainage (ARD).     

The geochemistry, mineralogy and maturity of gossans derived from volcanogenic Zn–Pb–Cu deposits of the eastern Lachlan Fold Belt, NSW, Australia

The Eastern Highlands of Australia have probably been in existence since the Late Cretaceous or earlier and so there has been ample time for mature gossan profiles to form over outcropping volcanogenic Zn–Pb–Cu mineralisation in the eastern Lachlan Fold Belt. The mature gossan profiles are characterised by the upward progression from supergene sulfides to secondary sulfates, carbonates and phosphates into a Fe-oxide dominated surficial capping which may contain boxwork textures after the original sulfides (as at the Woodlawn massive sulfide deposit). However, the region has locally been subjected to severe erosion and the weathering profile over many deposits is incomplete (immature) with carbonate and phosphate minerals, especially malachite, being found in surficial material. These immature gossans contain more Cu, Pb and Zn but lower As, Sn (and probably Au) than the mature gossans. Although Pb is probably the best single pathfinder for Zn–Pb–Cu VHMS deposits of the eastern Lachlan Fold Belt, Ag, As, Au, Bi, Mo, Sb and Sn are also useful, with most of these elements able to be concentrated in substantial amounts in Fe oxides and alunite–jarosite minerals.     

甘肃李坝金矿围岩蚀变与金成矿关系

西秦岭地区是目前国内造山型和卡林型金矿找矿的热点地区之一,已发现的甘肃李坝造山型金矿为超大型规模。以李坝金矿6号矿带为例,系统地研究了其蚀变矿物组合、近矿围岩蚀变分带及相应的金矿化特征,总结了矿床(带)的蚀变分带模式。该模式具典型的中心式环带结构,可分为3个蚀变带,由中心向外依次为黄铁绢英岩化带、绢云母化带和绿泥石化带。蚀变矿物组合分别为黄铁矿+绢云母+石英±毒砂±白云母±电气石±方解石、绢云母+绿泥石+石英+黄铁矿±黑云母及绿泥石+黑云母±绢云母±黄铁矿;与这3个蚀变带相对应的是金的富集带、矿化带和无矿带。蚀变岩石物质组分迁移分析表明,围岩蚀变及其分带是热水流体/岩石反应时岩石化学组分发生迁移的结果,矿化伴随着蚀变发生,且金矿化与黄铁矿化和浸染状硅化关系最为密切。     

安徽铜陵新桥Cu-Au-S矿床黄铁矿微量元素LA-ICP-MS原位测定及其对矿床成因的制约

激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)是一种固体微区分析新技术。用该技术来分析矿床中硫化物的微量元素组成可以为研究成矿流体特征、矿床成因及找矿勘探提供有关的科学信息。文中以安徽铜陵矿集区内新桥Cu-Au-S矿床中的黄铁矿为研究对象,在详细的野外观察和室内鉴定的基础上,将矿床中的黄铁矿分为具有沉积特征的胶状黄铁矿(PyⅠ)、具有变形重结晶和热液叠加作用特征的细粒他形黄铁矿(PyⅡ)和具热液成因特征的中—粗粒自形黄铁矿(PyⅢ)3种类型。LA-ICP-MS原位微量元素测定结果显示,PyⅠ中相对富含Ti、Co、Ni、As、Se、Te;PyⅡ继承了PyⅠ中富含Ti、Co、Ni、As、Se、Te、Bi的特征,同时还含有不均匀分布的少量成矿元素(Cu、Pb、Zn、Au、Ag);PyⅢ中成矿元素Cu、Pb、Zn、Ag、Au以及Bi元素的含量较高,Co、Ni、As的含量较低。在元素赋存状态方面,Co、Ni、As、Se和Te均以类质同象的形式进入到了黄铁矿的晶格中;Bi在PyⅡ中主要以含Bi矿物的微细包裹体形式存在,而在PyⅢ中的Bi还部分取代了Fe而占据了晶格;Cu、Pb、Zn、Au、Ag这些成矿元素中,Cu和Zn分别以黄铜矿和闪锌矿的矿物包裹体存在于黄铁矿中;PyⅡ中所含的少量Au、Ag,可能分别以自然金和自然银的形式存在,而在PyⅢ中Au可能主要以银金矿的形式存在,Ag除了以银金矿的形式存在以外还可能赋存于黄铁矿中含铋的矿物包裹体内;Pb主要赋存于黄铁矿中的方铅矿或含铋矿物的包裹体中。在综合分析黄铁矿的结构形态和微量元素组成特征的基础上认为,PyⅠ型黄铁矿可能形成于前人提出的晚古生代海底沉积或喷流沉积环境,PyⅡ和PyⅢ型黄铁矿分别形成于中生代区域构造变形-热液叠加改造的过渡环境和热液环境,PyⅡ和PyⅢ的形成时间相近。新桥矿床的形成可能经历了晚古生代海底沉积或喷流沉积期和燕山期热液期,胶黄铁矿主要形成于沉积成矿期,而矿床中成矿物质Cu、Pb、Zn、Au、Ag等主要来自燕山期岩浆侵入作用形成的热液成矿系统。     

广西中酸性岩浆岩风化区风化矿床类型及成矿作用研究

广西区内139个主要风化矿床(点)中有近4成集中分布于中酸性岩浆岩风化区。新近纪以来新构造运动活跃,东亚季风盛行产生了湿热气候,致使近2.0×105 km 2不同时代、不同岩性的中酸性岩浆岩广泛出露并遭受强烈风化,大面积的厚层风化壳在低山丘陵地貌景观区得以保存,这为风化矿床的发育提供了得天独厚的气候、地质、构造和地貌等条件。广西中酸性岩浆岩风化作用形成的矿床主要包括残积型(以钛铁砂矿为代表)、淋积型(以离子吸附型稀土矿为代表)和残余型(以高岭土矿和膨润土矿为代表)三个类型。这些不同类型的风化矿床在成矿条件上表现出显著的母岩专属性和风化环境偏在性,二者联合约束了风化矿床的成矿作用及成矿类型。风化过程中复杂的水岩反应(淋积作用、残积作用和残余作用)是导致中酸性岩浆岩风化形成各类矿床的内在机制。     

金窝子金矿金的赋存状态和金矿物特征

金窝子金矿属于岩浆热液型金矿床,金矿化类型有石英脉型和蚀变糜棱岩型.金多呈独立金矿物形式出现,少许呈分散状,以银金矿为主,次为自然金,平均成色782.金矿物以粒间金、裂隙金、连生金和包体金等形式嵌布于黄铁矿、石英、方铅矿及闪锌矿等主要载金矿物中,且黄铁矿、石英较金属硫化物中占优势,黄铜矿中未见金矿物.金矿物形态各样,粒度以中细粒为主.金矿物特征反映出本区金矿床的成矿物质主要来源于变质岩,成矿作用与华力西、燕山期中酸性侵入岩有关.这与地质地球化学研究所获得的矿床成因认识相一致.