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1.
The Elura Zn-Pb-Ag deposit, situated 43 km NNW of Cobar, western New South Wales, is hosted by the C.S.A. Siltstone, a distal turbidite sequence. Deep weathering has given rise to a bleached quartz-muscovite-kaolinite rock to a depth of approximately 80 m. Weathered bedrock is mantled by a thin (0.3–2 m) layer of soil and transported overburden which contains thin layers of maghemite-bearing gravels. Outcrop in the area is extremely poor with the insignificant gossan subcrop covered by 0.2 m of soil. The water table is presently at a depth of about 80 m. Groundwater is saline with up to 2.5% total dissolved solids.Oxidation of the orebody has resulted in the formation of a gossan and ferruginization of wall rocks. Elements associated with ore and retained at high concentration in the gossan are Ag, As, Ba, Cu, Hg, Mo, Pb, Sb, (Se) and Sn; much of the Zn has been leached whilst Cd and Tl are below the detection limits. Silver, Cu and Hg have been partially leached and concentrated in the supergene zone. Ferruginous wall rock contains substantial amounts of Pb, As and Ba but other element contents are substantially lower than in the gossan.Secondary dispersion from the Elura orebody is largely restricted to an interpreted paleodrainage channel SW of the orebody and has occurred in two distinct periods. Mobile elements, particularly Zn, leached during gossan formation, occur in anomalous concentrations at or near the water table. More recently, the less mobile elements Pb, As, Bi, Hg and Sb have been leached from mechanically transported fragments of ferruginized wall rock and gossan by the saline groundwaters and occur as anomalies up to 150 m from the gossan in near-surface bedrock. Copper and Zn form broad low-contrast anomalies whilst Sn is retained within the gossan.Iron-rich bands, 50–1200 mm in thickness, which are common in the weathered zone about the Elura orebody, were formed by precipitation from groundwater passing along bedding planes, shears, fractures and cracks. They have higher As, Bi, Co, Cu, Mn, Ni, Zn, lower values of Ba and Sr, and similar Pb, Sb and Sn contents to the weathered siltstones. Iron may be derived from Fe-rich carbonates in the siltstones and be redeposited as goethite and minor hematite. These Fe-rich bands have trapped target and pathfinder elements which are believed to be from primary haloes rather than from the orebody or gossan.A two-stage mechanism for the formation of some secondary minerals within the weathered zone has been confirmed by stable light isotope studies. These studies have also shown that fractionation of S isotopes is minimal during gossan formation, and that a S isotopic halo in weathered bedrock may be used as an exploration tool.  相似文献   

2.
Oxidation of the relatively iron sulfide-poor Dugald River zinc-lead lode in northwest Queensland and reaction of the acid solutions with carbonate has resulted in an undifferentiated gossan profile. The gossan is composed predominantly of quartz, goethite, hematite, barite, adularia, plumbian jarosite, plumbogummite and minor mica, chlorite, kaolinite and montmorillonite. Barite and adularia are formed by the breakdown of the barium feldspar hyalophane (K, Na, Ba)[(Al, Si)4O8] which occurs in the lode.Lead in the gossan is contained within the secondary minerals plumbogummite and plumbian jarosite, and in traces of anglesite and cerussite, whereas Zn occurs in the barite, secondary lead minerals and coronadite structures, and is adsorbed by iron oxides, phyllosilicates and carbonaceous matter. Only traces of zinc minerals smithsonite, goslarite and hemimorphite were detected.Use of Gresens' general metasomatic equation has enabled quantitative determination of compositional changes resulting from the oxidation of the ore. Silicon, Al, Ti and Ba are essentially immobile under the mildly acidic oxidizing conditions. In decreasing order of mobility Cd, Ca, S, Na, K, Mn, Mg, Zn, Ni and Cu, together with CO2 and Tl, have been leached from the gossan profile, while Ag, Sb, Se, As, Fe and Pb appear to have been added to the gossan, notably in a zone of solution-deposited secondary minerals where they have been concentrated, possibly as a result of leaching from the surface gossan.  相似文献   

3.
The presence of base‐metal mineralization at Woodlawn was first recognised early in 1968 when a roadside reconnaissance geochemical sampling survey, conducted over felsic volcanic rocks in the Goulburn‐Tarago area, encountered anomalous B horizon soils containing up to 200 ppm Cu, 800 ppm Pb and 300 ppm Zn. Regional soil thresholds have been determined at 50 ppm Cu, 90 ppm Pb and 50 ppm Zn. Chip samples from the subsequently located gossan revealed up to 2000 ppm Cu, 8000 ppm Pb and 2000 ppm Zn, 500 ppm Sn, 25 ppm Ag and 3000 ppm As.

The first grid B horizon soil geochemical survey was conducted in 1968 over the gossan and surrounding area, and repeated with closer spaced sampling in the first half of 1970. The first survey delineated strong Cu (to 1000 ppm) and Pb (to 2500 ppm) anomalies coincident with the gossan zone, and intense hydromorphic zinc anomalies (to 3000 ppm) located down slope from the gossan in residual clay‐soils derived from dolerite bedrock. Threshold values have been determined at 140 ppm Cu, 700 ppm Pb and 580 ppm Zn. Ag and Sn in B horizon soils show pronounced anomalies coincident with the gossan and are suitable metals for geochemical target definition. Of fourteen trace elements determined in 1974 from B and C horizon soils on two lines across the ore zone Cu, Pb, Zn, Se, Ba, Sn and Ag show direct correlation with the mineralization, whereas Cd and Mn show moderate hydromorphic dispersion, having accumulated principally in clay soils derived from dolerite weathering. As, Sb and Bi, whilst responding over the ore zone, show elevated values in soils over hanging‐wall units; Ni and Co show maximum levels in soils over dolerite bedrock.

Bark and leaves of Acacia mearnsii, collected from a line across the gossan, contain anomalous levels of Cu, Pb, Zn, Sn and Ti near the ore zone, and weaker, but clearly anomalous Mn and Ni levels over dolerite bedrock. Both bark and leaves of Acacia mearnsii reflect the presence of concealed mineralization. The shrub Solanum linearifolium grows preferentially over and close to the Woodlawn ore zone, where it contains up to 840 ppm Cu, 250 ppm Pb, 7300 ppm Zn, 6 ppm Sn and 250 ppm Ti in leaf ash compared with levels of 200 ppm Cu, 2 ppm Pb, 400 ppm Zn, 0.8 ppm Sn and 60 ppm Ti in plants growing 1.5 km from the ore zone. This shrub has potential as an indicator of base‐metal mineralization.  相似文献   

4.
Primary massive sulfide gossans (MSG) in the Bathurst Mining Camp (BMC), New Brunswick, Canada, are characterized by relative enrichment of Au, Sb, and As, formation of jarosite group minerals (jarosite, plumbojarosite, and argentojarosite) and little or no fractionation in the rare earth elements (REE), including preservation of large positive Eu anomalies (average [Eu/Eu*]NASC = 4.14 in MSG; 6.61 in massive sulfide mineralization; 0.60 in host rocks). The chemical and mineralogical characteristics of MSG (e.g., Halfmile Lake deposit) imply low pH (<3) and relatively oxidizing conditions during gossan formation; oxidation of a volcanogenic massive sulfide body (comprising pyrite, pyrrhotite, sphalerite, galena, and chalcopyrite) with a falling water table. The lack of light REE or heavy REE fractionation and preservation of positive Eu anomalies characteristic of the original (465 Ma) hydrothermal fluid is consistent with relatively large water-rock ratios during massive sulfide mineralization oxidation, and removal of the REE predominantly as sulfate complexes (LnSO4+, Ln(SO4)2−). Low pH groundwaters recovered from past producing mines in the BMC display REE patterns reflecting those inferred to have occurred during gossan formation. Gossan at the Restigouche deposit, in contrast to the Halfmile Lake deposit, displays mineralogical and chemical evidence for having been chemically reworked since primary gossan formation. Evidence for chemical reworking includes loss of primary massive sulfide mineralization textures, replacement of plumbojarosite with anglesite, almost complete removal of jarosite minerals, loss of Au, Sb, and As and apparent preferential removal of Eu, resulting in loss of positive Eu anomalies for most samples (average [Eu/Eu*]NASC = 1.21 in the gossan, with many displaying strong negative anomalies; 3.65 in massive sulfide mineralization; 0.54 in host rocks). Based on geochemical modeling, conditions inferred for the chemical reworking of the Restigouche deposit include near neutral conditions and either relatively oxidizing conditions with Eu2+ hosted in a preferentially weathered mineral host (possibly through substitution for Pb in plumbojarosite and beudantite) or cycling between reduced and oxidized conditions during gossan reworking.  相似文献   

5.
The Cu-Zn-Pb-Ag sulphide deposit at Teutonic Bore is a stratiform deposit of apparent volcanogenic origin in Archaean metabasaltic rocks in the Yilgarn Block of Western Australia. The area has moderate topographic relief, and has been weathered to a depth of about 75 m, which is about 40 m below the present water table. Part of the deposit, before mining commenced, was exposed at the surface as a gossan, samples of which contained between 500 and 1000 ppm Zn, Cu and Sb, and in excess of 1000 ppm Pb, Sn and As.The primary ore has weathered to supergene sulphides, then to an oxide assemblage containing abundant secondary ore minerals, then to leached oxides, and finally to surface gossan. The strong geochemical signature of the gossan is attributed partly to elements chemically combined with Fe oxides, partly to the presence of several stable secondary ore minerals, and partly to the presence of unweathered primary minerals. Diagnostic boxwork textures, except for those of pyrite, are not well developed.  相似文献   

6.
Despite having been a target for volcanic-hosted massive sulfide (VHMS) deposits since the 1960s, few resources have been defined in the Archean Yilgarn Craton of Western Australia. Exploration challenges associated with regolith and deep cover exacerbate the already-difficult task of exploring for small, deformed deposits in stratigraphically complex, metamorphosed volcanic terranes. We present results of drill-core logging, petrography, whole-rock geochemistry and portable X-ray Fluorescence data from the King Zn deposit, to help refine mineralogical and geochemical halos associated with VHMS mineralisation in amphibolite-facies greenstone sequences of the Yilgarn Craton. The King Zn deposit (2.15?Mt at 3.47?wt% Zn) occurs as a 1–7 m-thick stratiform lens dominated by iron sulfides, in an overturned, metamorphosed volcanic rock-dominated sequence located ～140?km east of Kalgoorlie. The local stratigraphy is characterised by garnet-amphibolite and strongly banded intermediate to felsic schists, with rare horizons of graphitic schist and talc schist. Massive sulfide mineralisation is characterised by stratiform pyrite–pyrrhotite–sphalerite at the contact between quartz–muscovite schists (‘the footwall dacite’), and banded quartz–biotite and amphibole?±?garnet schists of the stratigraphic hanging-wall. A zone of pyrite–(sphalerite) and pyrrhotite–pyrite–(chalcopyrite) veining extends throughout the stratigraphic footwall. Footwall garnet-amphibolites are of sub-alkaline basaltic affinity, with a central zone dominated by chlorite?±?magnetite interpreted to represent the Cu-bearing feeder zone. SiO2, CaO, Fe2O3T, MgO and Cu concentrations are highly variable, reflecting quartz–epidote?±?chlorite?±?magnetite?±?sulfide alteration. Hydrothermal alteration in stratigraphically overlying intermediate to felsic rocks is characterised by a mineral assemblage of quartz–muscovite?±?chlorite?±?albite?±?carbonate. Cordierite and anthophyllite are locally significant and indicative of zones of Mg-metasomatism prior to metamorphism. Increases in SiO2, Fe2O3T, pathfinder elements (e.g. As, Sb, Tl), and depletions of Na2O, CaO, Sr and MgO occur in quartz–muscovite schists approaching massive sulfide mineralisation. Within all strata (including the immediate hanging-wall), the following pathfinder elements are strongly correlated with Zn: Ag, As, Au, Bi, Cd, Eu/Eu*, Hg, In, Ni, Pb, Sb, Se and Tl. These geochemical halos resemble less metamorphosed VHMS deposits across the Yilgarn Craton and suggest that although metamorphism leads to element mobility and mineral segregation at the thin-section scale, assay samples of ～20?cm length are sufficient to vector to mineralisation in amphibolite facies greenstone belts. Recognition of minerals such as Mg-chlorite, muscovite, cordierite, anthophyllite, biotite/phlogopite, and abundant garnet are significant, in addition to Al-rich phases (i.e. kyanite, sillimanite, andalusite and/or staurolite) not identified at King. Chemographic diagrams may be used to identify and distinguish different alteration trends, along with several alteration indices (e.g. Alteration Index, Carbonate–Chlorite–Pyrite Index, Silicification Index) and the abundance of normative corundum and quartz.  相似文献   

7.
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.  相似文献   

8.
黄铁矿风化过程中元素的活性及对环境的影响   总被引：7，自引：0，他引：7       下载免费PDF全文
卢龙  王汝成  薛纪越  陈骏 《地质论评》2001,47(1):95-101
在对安徽铜陵鸡冠山硫铁矿尾矿中黄铁矿风化产物组构特征研究的基础上,划分出代表不同风化程度的4种矿石组构型,并进而对不同组构型中硫和金属元素的含量、宫集系数、流失系数变化进行了研究。研究表明在风化过程中,As、Sb、Cu、Zn明显富集,其中As、Cu、Zn对环境的潜在危害较Sb大;Co、Ni、Bi明显流失或严重流失,对环境已经形成污染,其中Bi的污染程度较高。  相似文献   

9.
All the Kamchatkan recent hydrothermal systems are restricted to two volcanic zones, Central Kamchatka of Late Miocene-Pliocene age and East Kamchatka, where several active volcanoes are located. Solutions from active hydrothermal systems commonly contain elements, including As, Sb, Hg, Li, Rb, Cs, B, Cu, Pb, Zn, Ag, Au,Sr and Ba, with the first seven predominating. Higher abundances of ore elements occur in active hydrothermal systems with solutions of sodium chloride composition. Those are the Kireunskaya, Dvukhyurtochnaya and Apapelskaya systems in the Central Kamchatka volcanic zone and the Uzon hydrothermal system in the East Kamchatka volcanic zone. The hydrothermal systems are restricted to structures having very long histories of evolution and which are characterized by contrasting types of magmatism. At present chemical precipitates and altered rocks with higher abundances of As, Sb and trace amounts of Au, Ag, Cu, Ph and Zn are forming in the discharge zones of these hydrothermal systems. Large zones of alterations (alunitic quartzites* and argillites) with high abundances of As, Sb, Hg, Cu, Pb, Ga and Zr occur in the Central Kamchatka volcanic zone. Here zones of mineralization (cinnabar, realgar, stibnite, orpiment, pyrite, chalcopyrite, sphalerite, galena) occur also; native gold, native silver and gudmundite occur rarely.In the recent Uzon caldera hydrothermal system, As-Sb-Hg mineralization with bitumen and oils is now forming. The ore deposit is zoned, with the most abundant ore minerals being realgar, uzonite, alacranite, stibnite and pyrite. Cinnabar, orpiment, marcasite and native mercury occur occasionally, and single grains of native gold, native silver and native copper are present. At present a total of 7000 t As, 350 t Sb and 200 t Hg have been deposited in the mineralization zone at geochemical boundaries. The general geological and geochemical data suggest that at depth the As-Sb-Hg mineralization may change to gold-silver mineralization.  相似文献   

10.
An elucidation of the background levels of heavy metals, including certain toxic elements, is very essential to accomplish an important environmental assessment. A regional geochemical mapping in Hokkaido, Japan was undertaken by the Geological Survey of Japan, AIST as part of a nationwide geochemical mapping for this purpose. There were 692 stream sediments collected from the active channel (1 sample) / (100 km2) in Hokkaido and the fine fraction sieved through a 180 μm screen was analyzed using the AAS, ICP-AES, and ICP-MS techniques. The regional geochemical maps for 51 elements were created as a 2000 m mesh map using the geographic information system software. Spatial distribution patterns of elemental concentrations in stream sediments, particularly Neogene–Quaternary volcanic and pyroclastic rocks, are primarily determined by surface geology. The correspondence of elemental concentrations in stream sediments to parent lithology is clearly indicated by ANOVA and a multiple comparison. Sediment samples supplied from mafic volcanic and felsic–mafic pyroclastic rocks are significantly rich in MgO, Al2O3, P2O5, CaO, Sc, TiO2, V, MnO, Total (T)-Fe2O3, Co, Zn, Sr, and heavy rare earth elements (REEs) (Y and Eu–Lu), but significantly lacking in alkali elements, Be, Nb, light REEs (La–Nd), Ta, Tl, Th, and U. Accretionary complexes with sedimentary rocks derived from sediments are in stark contrast to volcanic and pyroclastic rocks. Accretionary complexes with mafic–ultramafic rock have significantly elevated Nb, Ta, and Th abundances in sediments besides MgO, Cr, Ni, Co, and Cu. This inexplicable result is caused by the mixed distributions of granite and ultramafic–mafic rocks.The watersheds with mineral deposits relate to the high concentrations of certain elements such as Zn, As, and Hg. The geochemically anomalous pattern, which is a map of the regional anomalies, and a scatter diagram were applied to examine the contribution of mineral deposits to MnO, T-Fe2O3, Cr, Cu, Zn, As, Cd, Sb, Hg, Pb, and Bi concentrations. Consequently, they were grouped into four types: 1) Mineral deposits with no outliers resulting from mineralization (MnO, T-Fe2O3, and Cr), 2) sediments supplied from watersheds without metal deposits conceal high metal inputs from known mineral deposits (Cu), 3) deposits from a geochemically anomalous area that closely relates to the presence of mineral deposits (As, Sb, and Hg), and 4) deposits from the widely altered zone associated with the Kuroko as well as hydrothermal deposits corresponding to geochemically anomalous patterns (Zn, Cd, and Pb). This study provides an important regional geochemical database for a young island-arc setting and interpretational problems, such as complicated geology and active erosion, that are unique to Japan.  相似文献   

11.
上盘围岩是矿床钻探过程中首先遇到的围岩,研究其蚀变特征具有重要的找矿指导意义。对胶东西北部露天开采的仓上金矿床的详细研究表明,上盘围岩蚀变以绿泥石化为主,蚀变分带自远矿端到近矿端依次为方解石绿泥石化带、赤铁矿绿泥石化带、绿帘石化带和绢英岩化带。黄铁矿的形态、成分和热电性标型显示,成矿过程中上盘围岩提供了丰富的Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｐｂ、Ｚｎ和Ａｕ、Ｐｔ等。上盘围岩的近矿标志是绢英岩化增强,黄铁矿的｛１００｝＋｛２１０｝增多,Ｓ、Ｃｕ、Ｐｂ、Ｚｎ和Ａｕ、Ｐｔ增高,Ｓ／Ｆｅ离子比和ｗ（Ｃｏ＋Ｎｉ）／ｗ（Ａｓ＋Ｓｂ）降低,Ｐ型黄铁矿出现率增高,蚀变岩的金含量增高。  相似文献   

12.
Gossans associated with the Dugald River zinc-lead lode contain anomalous concentrations of Zn, Pb, Ag, As, Cd, Cu, Sb, Se, Tl and Ba and differ from those on the more pyritic Western Lode (Zn, Pb, Cu, As, Tl) and those associated with copper mineralization in the hanging wall (As, Bi, Co, Cu, Mo, Ni, Sb). Mineralogical and geochemical variations in gossans along strike reflect changes in primary ore and gangue mineralogy, particularly towards the north, where the Dugald River lode and hanging wall copper mineralization merge. Leaching of more soluble elements from the surface and re-precipitation below have resulted in large geochemical variations in the top metre of the profile.Dispersion into wall rocks has occurred over two distinct periods: hydromorphic dispersion, before erosion removed much of the gossan and surrounding Corella Formation, has resulted in very high Zn contents (up to 9%) in the footwall, whereas a more even dispersion of target and pathfinder elements into hanging and footwall rocks is from recent weathering of the slightly elevated gossan.  相似文献   

13.
本文对浙江省绍兴一龙泉隆起带内代表性金矿床的原生及次生地球化学异常特征进行了系统研究,确定了异常中最主要的指示元素以及它们自近矿至远矿、从矿下到矿上的分带序列和组合特征,并总结出在本区及邻区金矿勘查中具有实际意义的综合地球化学找矿标志。  相似文献   

14.
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.  相似文献   

15.
In the oxidation zone of the Berezovskoe gold deposit in the middle Urals, Russia, minerals of the beudantite–segnitite series (idealized formulas PbFe3 3+ AsO4)(SO4)(OH)6 and PbFe3 3+ AsO4)(AsO3OH)(OH)6, respectively) form a multicomponent solid solution system with wide variations in the As, S, Fe, Cu, and Sb contents and less variable P, Cr, Zn, Pb, and contents K. The found minerals of this system correspond to series from beudantite with 1.25 S apfu to S-free segnitite, with segnitite lacking between 1.57 and 1.79 As apfu. Segnitite at the Berezovskoe deposit contains presumably pentavalent Sb (up to 15.2 wt % Sb2O5 = 0.76 Sb apfu, the highest Sb content in the alunite supergroup minerals), which replaces Fe3+. The Sb content increases with increasing As/S value. On the contrary, beudantite is free of or very poor in Sb (0.00–0.03 Sb apfu). Many samples of segnitite are enriched in Cu (up to 8.2 wt% CuO = 0.83 Cu apfu, uncommonly high Cu content for this mineral) and/or in Zn (up to 2.0 wt% ZnO = 0.19 Zn apfu). Both Cu and Zn replace Fe. The generalized formula of a hypothetic end member of the segnitite series with 1 Sb apfu is Pb(Fe3+ M 2+Sb5+)(AsO4)2(OH)6, where M = Cu, Zn, Fe2+. The chemical evolution of beudantite–segnitite series minerals at the Berezovskoe deposit is characterized by an increase in the S/As value with a decrease in the Sb content from early to late generations.  相似文献   

16.
Six epizonal gold deposits in the 30-km-long Yangshan gold belt, Gansu Province are estimated to contain more than 300 t of gold at an average grade of 4.76 g/t and thus define one of China's largest gold resources. Detailed paragenetic studies have recognized five stages of sulfide mineral precipitation in the deposits of the belt. Syngenetic/diagenetic pyrite (Py0) has a framboidal or colloform texture and is disseminated in the metasedimentary host rocks. Early hydrothermal pyrite (Py1) in quartz veins is disseminated in metasedimentary rocks and dikes and also occurs as semi-massive pyrite aggregates or bedding-parallel pyrite bands in phyllite. The main ore stage pyrite (Py2) commonly overgrows Py1 and is typically associated with main ore stage arsenopyrite (Apy2). Late ore stage pyrite (Py3), arsenopyrite (Apy3), and stibnite occur in quartz ± calcite veins or are disseminated in country rocks. Post-ore stage pyrite (Py4) occurs in quartz ± calcite veins that cut all earlier formed mineralization. Electron probe microanalyses and laser ablation-inductively coupled plasma mass spectrometry analyses reveal that different generations of sulfides have characteristic of major and trace element patterns, which can be used as a proxy for the distinct hydrothermal events. Syngenetic/diagenetic pyrite has high concentrations of As, Au, Bi, Co, Cu, Mn, Ni, Pb, Sb, and Zn. The Py0 also retains a sedimentary Co/Ni ratio, which is distinct from hydrothermal ore-related pyrite. Early hydrothermal Py1 has high contents of Ag, As, Au, Bi, Cu, Fe, Sb, and V, and it reflects elevated levels of these elements in the earliest mineralizing metamorphic fluids. The main ore stage Py2 has a very high content of As (median value of 2.96 wt%) and Au (median value of 47.5 ppm) and slightly elevated Cu, but relatively low values for other trace elements. Arsenic in the main ore stage Py2 occurs in solid solution. Late ore stage Py3, formed coevally with stibnite, contains relatively high As (median value of 1.44 wt%), Au, Fe, Mn, Mo, Sb, and Zn and low Bi, Co, Ni, and Pb. The main ore stage Apy2, compared to late ore stage arsenopyrite, is relatively enriched in As, whereas the later Apy3 has high concentrations of S, Fe, and Sb, which is consistent with element patterns in associated main and late ore stage pyrite generations. Compared with pyrite from other stages, the post-ore stage Py4 has relatively low concentrations of Fe and S, whereas As remains elevated (2.05～3.20 wt%), which could be interpreted by the substitution of As? for S in the pyrite structure. These results suggest that syngenetic/diagenetic pyrite is the main metal source for the Yangshan gold deposits where such pyrite was metamorphosed at depth below presently exposed levels. The ore-forming elements were concentrated into the hydrothermal fluids during metamorphic devolatilization, and subsequently, during extensive fluid–rock interaction at shallower levels, these elements were precipitated via widespread sulfidation during the main ore stage.  相似文献   

17.
The Zheyaoshan deposit is the largest within the Baiyinchang (BYC) volcanic-hosted massive sulfide (VHMS) district, located in the northern Qilian orogenic belt of North China. The deposit is hosted by quartz keratophyre tuffs, with wall-rock alteration mainly comprising chlorite, sericite, quartz, pyrite and epidote. Mineral assemblages within the altered host rocks can be divided into a sericite-quartz-dominant assemblage (sericite-silicified zone), a chlorite-dominant assemblage (chlorite-dominant zone) and a pyrite-dominant assemblage (mineralized zone) based on geochemical analysis and alteration characteristics. We have conducted detailed processing and critical analysis of the geochemical data of both the altered and least-altered host rocks in order to investigate the problem of closure in the geochemical dataset to eliminate the influence that each component has on the other in terms of mass change, and have applied the standardized method of the mass change calculation to analyze this data. The results show that: (1) the sericite-silicified zone formed along fissures due to the ingress of hydrothermal fluids, with MnO2, Na2O and CaO being mobilized into the hydrothermal fluids leached and MgO, Fe2O3, SiO2, K2O, BaO deposited. Additionally, Ag, Cu and chalcophile elements (Ag, As and Bi) were enriched while Pb, Zn and large ion lithophile elements (LILEs) (Cs, Sr, Eu, Be) were mobilized into hydrothermal fluids; (2) the physiochemical conditions and pH levels of the hydrothermal fluids changed during sericitization, with MgO, Fe2O3, BaO being further enriched and MnO, Na2O, CaO further depleted, leading to formation of chlorite and the initial precipitation of metallogenic the (Cu, Zn, Pb) and chalcophile elements (Ag, As, Bi); (3) the negative Eu anomaly was mainly due to its strong activity when Eu is mobilized into the hydrothermal fluids during since plagioclase break-down during the sericite-silicification process; (4) AI and CCPI values gradually increase towards the orebody. The chlorite-dominant assemblage and sericite-quartz-dominant assemblage on the periphery of the chlorite-dominant zone can all be used as vectors towards the volcanic massive sulfide orebody and for regional-scale mineral exploration. Either leached elements or enriched elements can be considered as significant indicator elements and as prospective indicators for geochemical exploration within the BYC district. The Eu anomaly may be especially useful as an indicator for distinguishing the least-altered rocks which has great significance for exploration on the regional scale.  相似文献   

18.
通过对东昆仑-阿尔金地区区域化探工作研究程度及取得主要成果的介绍,说明了该区开展区域化探工作所采用关键技术方法的有效性,并大致阐述了本区39种元素的富集特征及其分带性。通过研究认为,东昆仑-阿尔金地区是铅、锌、铁、铜、金、银、钨、钼、锡、锑、汞等多元素的富集区,东昆仑祁漫塔格是以铅、锌、铁、铜、钨、锡、金等为主的多金属地球化学带,阿尔喀山一带则是东昆仑地区的主要汞、锑地球化学带,另外,阿尔金金、铜成矿带和阿帕-茫崖超基性岩带也是本区具有重要地质找矿意义的地球化学区带,上述研究成果对该区后继的地质找矿工作具有极高的指导意义和参考价值,亦为该区成为重要的整装勘查区和资源接替区奠定了基础。  相似文献   

19.
烂泥塘矿床是云南香格里拉地区典型的斑岩型铜矿床,主矿体产于在地表以下300～500米,地表矿化带仅见脉状铜矿体和铜矿化体.为研究云南香格里拉烂泥塘斑岩铜矿床的原生晕异常结构,本文以异常结构模式理论和方法为基础,对矿床地表和坑道岩矿石样品开展了元素组合、异常特征和水平分带规律研究.结果表明,烂泥塘铜矿床地球化学系统的结构...  相似文献   

20.
在进行原生晕元素分带研究时,所选元素多未进行筛选,不利于正确认识分带规律及指导矿产预测。本文基于扎家同哪金矿2779个钻孔样品数据,拟通过定量评价不同金属元素在围岩、矿化围岩、矿石等中的富集程度,研究不同元素在矿化过程中形成原生晕的能力差异。研究发现,扎家同哪金矿Au、As、Sb、Hg、W、Ag在围岩、矿化围岩和矿石中富集程度递增,易形成原生晕,Zn仅在矿石中富集,成晕规模有限,Mo、Cu、Pb、Sn富集微弱或表现为亏损,较难形成原生晕;扎家同哪金矿不同位置与成矿有关的富集元素为Au、As、Sb(围岩)—Au、As、Sb、W、Hg(Ag)(矿化围岩)—Au、As、Ag、Sb、W、Hg、Zn(矿石),成矿过程中元素在矿化围岩中富集的权重由大至小为As、Hg、Au、Sb、W、Mo、Sn、Pb、Zn、Cu、Ag,进入围岩能力总体表现为低—高—中温元素递减的趋势。对于扎家同哪金矿,在研究原生晕分带特征、指导进一步找矿时,宜优先选用As、Hg、Au、Sb和W等元素。  相似文献   

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