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1.
《Ore Geology Reviews》2010,37(4):293-305
A centrographic method for analysing mineral deposit clusters is illustrated using the komatiite-hosted Kambalda nickel sulphide deposit cluster, Yilgarn craton, Western Australia. In this method, the standard distance circle divides the cluster into a more endowed inner part and a less endowed peripheral part. The standard deviational ellipse, another centrographic object, depicts the preferred northwest–southeast trend of nickel orebodies at Kambalda. Weighted centrography shows that nickel endowment is greater in the eastern than western part of the cluster. The spatio-geometric interaction of the circle and ellipse splits the cluster into several partitions. The relative concentration of nickel orebodies or endowment within a partition in relation to their concentration within the entire cluster is termed ‘capture efficiency’. Komatiite areal trace exhibits higher nickel orebody capture efficiency than spatio-geometric partitions; however, some spatio-geometric partitions exhibit nickel endowment capture efficiencies comparable to that of komatiite. Furthermore, nickel orebody and endowment capture efficiencies of komatiite are elevated only within the standard distance circle. These results suggest that at Kambalda, (i) the standard distance circle is a prime window for understanding the komatiite-hosted nickel system, and (ii) spatio-geometric partitions are plausible locales for spatial analysis of nickel orebodies and endowment. The proposed centrographic method is potentially useful in mineral resource estimations and mineral exploration targeting. 相似文献
2.
The use of Shortwave Infrared (SWIR) and Thermal Infrared (TIR) hyperspectral data in mineral exploration has been well documented in many mineralisation types, but is limited in komatiite-hosted nickel sulphide deposits. This project combines hyperspectral, Portable X-ray Fluorescence (pXRF) and whole-rock geochemical data to assess different analytical techniques in the exploration of these deposits. We use the Fisher East nickel sulphide prospects, Western Australia for our case study. The Fisher East prospects lie in an area of the eastern goldfields that has historically been underexplored and understudied. The rocks have undergone intense deformation with primary igneous textures being destroyed, along with strong alteration to talc carbonate assemblages. Combining different analytical tools allowed for differentiation of A and B-zones of original komatiite flows, and the reconstruction of original volcanological facies in a setting where whole rock chemistry as well as igneous textures have been substantially modified by metamorphism. By using different lithogeochemical techniques including pXRF, this study shows the Fisher East prospects are hosted within channelised komatiite flows, and have similar characteristics to Kambalda style deposits. 相似文献
3.
Paul Duuring Wouter Bleeker Steve W. Beresford Nicholas Hayward 《Mineralium Deposita》2010,45(3):281-311
Perseverance is a world-class, komatiite-hosted nickel sulphide deposit situated in the well-endowed Leinster nickel camp
of the Agnew–Wiluna greenstone belt, Western Australia. The mine stratigraphy at Perseverance trends north-northwest (NNW),
dips steeply to the west, and is overturned. Stratigraphic footwall units lie along the western margin of the Perseverance
Ultramafic Complex (PUC). The PUC comprises a basal nickel sulphide-bearing orthocumulate- to mesocumulate-textured komatiite
that is overlain by a thicker, nickel sulphide-poor, dunite lens. Hanging wall rocks include rhyodacite that is texturally
and compositionally similar to footwall volcanic rocks. These rocks separate the PUC from a second sequence of nickeliferous,
E-facing, spinifex-textured komatiite units (i.e. the East Perseverance komatiite). Past workers argue for a conformable stratigraphic
contact between the PUC and the East Perseverance komatiite and conclude that the PUC is extrusive. This study, however, clearly
demonstrates that these komatiite sequences are discordant, implying that the PUC may have intruded rhyodacite country rock
as a sill with subsequent structural juxtaposition against the East Perseverance komatiite. Early N–S shortening associated
with the regional DI deformation event (corresponding to the local DP1 to DP3 events at Perseverance) resulted in the heterogeneous partitioning of strain along the margins of the competent dunite. A
mylonite developed in the more ductile footwall rocks along the footwall margin of the PUC, while isoclinal F3 folds, such as the Hanging wall limb and Felsic Nose folds, formed in low-mean stress domains along the fringes of the elongated
dunite lens. Strata-bound massive and disseminated nickel sulphides were passively fold thickened in hinge areas of isoclinal
folds, whereas basal massive sulphides lubricated fold limbs and promoted thrust movement along shallowly dipping lithological
contacts. Massive sulphides were physically remobilised up to 20 m from their primary footwall position into deposit-scale
fold hinges to form the 1A and Felsic Nose orebodies. First-order controls on the geometry of the Perseverance deposit include
the thermomechanical erosion of footwall rocks and the channelling of the mineralised komatiitic magma. Second- or third-order
controls are several postvolcanic deformation events, which resulted in the progressive folding and shearing of the footwall
contact, as well as the passive fold thickening of massive and disseminated sulphide orebodies. Massive sulphides were physically
remobilised into multiple generations of fold hinges and shear zones. Important implications for near-mine exploration in
the Leinster camp include identifying nickeliferous komatiite units, defining their three-dimensional geometry, and targeting
fold hinge areas. Fold plunge directions and stretching lineations are indicators of potential plunge directions of massive
sulphide orebodies. 相似文献
4.
Estimating the undiscovered mineral resources of a terrane is a challenging, yet essential, task in mineral exploration. We
apply Zipf’s law rank statistical analysis to estimate the undiscovered nickel sulphide resources in the Norseman-Wiluna Greenstone
Belt, Western Australia. The analysis suggests that about 3.0 to 10.0 Mt of nickel sulphide resources are yet to be discovered
in this belt, compared to the currently known total nickel sulphide endowment of 10.8 Mt. This undiscovered nickel sulphide
endowment is likely to be hosted by incompletely delineated deposits and undiscovered deposits in less explored komatiites
in the belt. Using the more detailed data subset of the Kambalda domain, this study manipulates Zipf’s law to estimate the
sizes of undiscovered deposits, in addition to the domain’s total nickel sulphide endowment estimate. Importantly, regression
analysis shows that the gradient of the line of best fit through the logarithmic rank-size plot for the detailed Kambalda
data subset is −1. This gradient, which is the key Zipf’s law constant k, has the value of −0.92 for the Norseman-Wiluna Greenstone Belt which is collectively less mature than the Kambalda domain.
This result corroborates the use of k = −1 in Zipf’s law predictive analyses of mineral resources for deposit populations for which the value of k = −1 has not yet been attained due to exploration immaturity. 相似文献
5.
The Black Swan komatiite sequence, in the Eastern Goldfields province of the Archaean Yilgarn Craton in Western Australia, is a body of dominantly olivine-rich cumulates with lesser volumes of spinifex textured rocks, interpreted as a section through an extensive komatiite lava flow field. The sequence hosts a number of nickel sulfide orebodies, including the Silver Swan massive shoot and the Cygnet and Black Swan disseminated orebodies. The massive sulfide orebodies of the Black Swan Succession are pervasively depleted in all platinum group elements (PGEs), particularly Pt and Pd, despite very high Ni contents. This depletion cannot be explained by R-factor variations, which would also require relatively low Ni tenors. The PGE depletion could be explained in part if the ores are enriched in a monosulfide solid solution (MSS) cumulate component, but requires some additional fractional segregation of sulfide melt upstream from the site of deposition. The Silver Swan orebody shows a remarkably consistent vertical zonation in PGE contents, particularly in Ir, Ru, Rh, Os, which increase systematically from very low levels at the stratigraphic base of the sulfide body to maxima corresponding roughly with the top of a lower layer of the orebody rich in silicate inclusions. Platinum shows the opposite trend, but is somewhat modified by remobilisation during talc carbonate alteration. A similar pattern is also observed in the adjacent White Swan orebody. This zonation is interpreted and modelled as the result of fractional crystallisation of MSS from the molten sulfide pool. The strong IPGE depletion towards the base of the orebody may be a consequence of sulfide liquid crystallisation in an inverted thermal gradient, between a thin rapidly cooling upper rind of komatiite lava and a hot substrate.Electronic Supplementary Material Supplementary material is available in the online version of this article at Editorial handling: Peter Lightfoot 相似文献
6.
The 18 m-long UWA-04-02 drillcore from the Fe-Ni-Cu-PGE Wannaway deposit in the Widiemooltha Dome district (Eastern Goldfields, Western Australia) intersects the whole sequence of a komatiite-hosted layer of metal-rich sulfide magma. In spite of regional deformation and amphibolite facies metamorphism the sequence in the drillcore still preserves some of the original, magmatic textures and assemblages and these were examined in a great detail. The magmatic orebody typically consists of basal massive sulfides grading to net-textured (matrix) and disseminated sulfide mineralization upward into the komatiite host. The ore zone is underlined by sulfide-rich black shale passing to basalts. Country rock xenoliths are locally enclosed in the massive sulfides. Portions of the drillcore untouched by penetrative deformation and with minimal imprint by late-stage serpentinization allow the construction of a fairly complex framework where mineral assemblages and mineral chemistry of sulfides, spinels and silicates vary systematically with stratigraphy and may reflect original conditions of ore deposition. The general ore assemblage is dominated by Fe-sulfide and pentlandite, with minor sphalerite and chalcopyrite, spinels (Zn-rich chromite, Ti-magnetite), alabandite (MnS), accessory PGE-rich sulfarsenides and tellurides and rare molybdenite. Monoclinic and high-S hexagonal pyrrhotite and fresh Zn-Mn-rich chromite characterize the basal massive facies, whereas the matrix ore facies is marked by magnetite, sphalerite and a gradually S-depleted and reduced assemblage now represented by troilite exsolving low-S hexagonal pyrrhotite and alabandite. Compositional modifications of the Fe-sulfides across the whole orebody and occurrence of alabandite testify to progressive sulfur loss concomitant with the establishment of low fO2 conditions over several meters upsequence in the matrix ore facies. PGE-rich sulfarsenides disseminated across the whole mineralized sequence display igneous textures and PGE fractionation trends. The composition of olivine intergrown with matrix sulfides and in the serpentinized hangingwall komatiite deviates from the typical unmetamorphosed komatiite-related, highly-forsteritic type. However the Fe, Mn and Zn contents of olivine crystals decrease systematically and gradually with distance from mineralization towards the hangingwall komatiite. Contamination may be an alternative to metamorphic recrystallization of olivine as the cause of these trends. The role of contamination is also shown by the trends of whole-rock data from the mineralized sequence across the entire drillcore. Textures and mineral chemistry of minerals from the different rock facies in the drillcore are evaluated in terms of metamorphic effects, although the remarkable relationship observed between stratigraphy and several major and accessory phases over metric distances is suggestive of alternative options including primary processes involving the komatiitic lava flow in its interaction both with the black shale substrate and with the sulfide melt ponding at its base. 相似文献
7.
江西省弋阳县大源岭瓷石矿是2009年江西省发现的重要矿产地之一。通过对矿区地质特征、矿体特征分析研究,大源岭瓷石矿为赋存侏罗系于林山组层间裂隙的岩浆侵入矿床,矿体厚度大、规模大、储量大,矿体与围岩接触界线清晰,容易辨认。通过对矿石特征以及加工技术性能的分析研究,瓷石矿石为绢云母化微细粒少斑花岗斑岩,三氧化二铝等粘土矿物含量高,铁主要以菱铁矿赋存,矿石质量好,为优质瓷石。矿石工业类型属硬质瓷石,矿床成因为岩浆自变质矿床。该矿床的发现不仅为江西省陶瓷产业发展提供了资源保障,而且为今后江西省乃至全国寻找同类型瓷石矿床有重要的现实指导意义。 相似文献
8.
通过系统采集紫金山铜金矿床4~11线共41个钻孔的岩矿样,绘制原生晕剖面图,建立垂向元素分带序列、矿体剥蚀程度准则,结合深部指示元素的特征,进行隐伏矿预测。该矿床金矿近矿晕为Au-Ag-Zn1,尾部晕为BiGa-Mo-Sn-Ti-Co-Ni-W1-V;铜矿前缘晕为Hg-Sb-As,近矿晕为Cu-Pb1-Zn2,尾部晕为Be-W2。矿体剥蚀程度评价表明,高硫型铜矿体往深部已尖灭。深部F-Mn-Pb2-Zn3的异常形态和元素组合符合典型斑岩矿床的外带特征,斑岩体延伸至矿床周边;深部的蚀变矿物组合、金属矿物组合、流体包裹体特征等均表明深部可能存在斑岩铜(钼)矿床。 相似文献
9.
黄铁矿热电性是矿床学及深部地质找矿的重要研究内容之一,该方法多应用于金矿床的地质勘探,而在铜矿床勘探中应用较少.滇中和尚洞铜矿床属于中高温热液矿床,矿体宏观地质条件差异小,深部找矿难度大,本文对该矿床Ⅰ号矿体开展了黄铁矿热电性特征及深部找矿预测研究.结果表明,该矿床黄铁矿热电系数分布呈现多峰组合,矿体铜矿化强度与黄铁矿... 相似文献
10.
Platinum group element and nickel sulphide ore tenors of the Mount Keith nickel deposit, Yilgarn Craton, Australia 总被引：1，自引：0，他引：1
A set of platinum group element (PGE) analyses of about 120 samples from a 250-m continuous drill core through the Mount Keith komatiite-hosted nickel orebody, combined with Ni, Cu, Co, S, and major elements, reveals a complex trend of covariance between the original cumulus components of a thick sequence of nearly pure olivine–sulphide liquid adcumulates. The intersection is divided into informal chemostratigraphic zones, defined primarily by combinations of fine-scale cyclicity in original olivine composition, defined by Mg#, and sulphide composition, defined by Pt/S and Ni/S. Contents of Ni and PGE in 100% sulphides (tenors) were determined from linear regressions of the Ni–S and PGE–S covariance for each zone. Inferred olivine compositions range from about Fo92 to Fo94.6 and show a broad decrease from bottom to top of the sequence complicated by numerous reversals, revealing crystallisation in an open conduit system. Ni and PGE tenors of Mount Keith sulphide ores have typical values similar to the type I deposits of the Kambalda Dome. Mobility of S, at least on the scale of 2-m sample composites, is evidently relatively minor. Tenors for the various zones range 12–22% Ni, 370–1540?ppb Pt, 970–3670?ppb Pd, 100–460?ppb Ir, 170–460?ppb Rh, and 710–1260?ppb Ru. Pt, Pd, and Rh tenors are very strongly correlated, but the iridium group of platinum group elements (IPGEs; Ir and Ru) less so. Tenor variations are predominantly controlled by variations in magma/sulphide ratio R (100–350), with a minor component of variance from equilibrium crystallisation trends in the parent magma. PGE depletion in the silicate melt due to sulphide liquid extraction is limited by entrainment of sulphide liquid droplets and continuous equilibration with the transporting silicate magma. Ratios of the PGEs to one another are similar to those in the host komatiite magma, with the exception of Pt, which is systematically depleted in ores, relative to Rh and Pd and relative to host magma, by a consistent factor of about 2 to 2.5. This anomalous Pt depletion relative to PGE element ratios in unmineralized komatiitic rocks matches that observed in bulk compositions of many komatiite-hosted orebodies. The highly consistent nature of this depletion, and particularly the very strong correlation between Pt, Pd, and Rh in the Mount Keith deposit, argue that this depletion is a primary magmatic signal and not an artefact of alteration. Differential diffusion rates between Pt and the other PGEs, giving rise to a low effective partition coefficient for Pt into sulphide liquid, is advanced as a possible but not definitive explanation. 相似文献
11.
红柳沟金矿床属中-低温热液构造破碎蚀变岩型金矿床,目前该矿床已经资源枯竭。为了更好地开展该矿床今后的找矿工作,综合分析了红柳沟金矿床的矿区地质特征、金矿体展布规律及找矿标志;并根据矿体特征、矿石质量、矿石矿物的生成顺序与形成阶段、金的赋存状态及围岩蚀变特征,简要地分析了矿床成因。研究认为,红柳沟金矿床的矿体受SN向的次级断裂构造控制,空间上具有向南侧伏现象,结合化探异常,加强沟南构造破碎蚀变带的深部找矿,将会大幅度提升该矿的远景储量。 相似文献
12.
The Black Swan komatiite sequence is a package of dominantly olivine-rich cumulates with lesser volumes of spinifex textured rocks, interpreted as a section through an extensive komatiite lava flow field. The sequence hosts a number of nickel sulfide orebodies, including the Silver Swan massive shoot and the Cygnet and Black Swan disseminated orebodies. A large body of whole rock analyses on komatiitic rocks from the Black Swan area has been filtered for metasomatic effects. With the exception of mobile elements such as Ca and alkalis, most samples retain residual igneous geochemistry, and can be modelled predominantly by fractionation and accumulation of olivine. Whole rock MgO–FeO relationships imply a relatively restricted range of olivine compositions, more primitive than the olivine which would have been in equilibrium with the transporting komatiite lavas, and together with textural data indicate that much of the cumulus olivine in the sequence was transported. Flow top compositions show evidence for chromite saturation, but the cumulates are deficient in accumulated chromite. Chromite compositions are typical of those found in compound flow-facies komatiites, and are distinct from those in komatiitic dunite bodies. Incompatible trace element abundances show three superimposed influences: control by the relative proportion of olivine to liquid; a signature of crustal contamination and an overprint of metasomatic introduction of LREE, Zr and Th. This overprint is most evident in cumulates, and relatively insignificant in the spinifex rocks. Platinum and palladium behaved as incompatible elements and are negatively correlated with MgO. They show no evidence for wholesale depletion due to sulfide extraction, which was evidently restricted to specific lava tubes or pathways. The lack of correspondence between PGE depletion and contamination by siliceous material implies that contamination alone is insufficient to generate S-saturation and ore formation in the absence of sulfide in the assimilant. Contamination signatures in spinifex-textured rocks may be a guide to Ni-sulfide mineralisation, but are not entirely reliable in the absence of other evidence. The widespread vesicularity of the sequence may be attributable to assimilated water rather than to primary mantle-derived volatiles, and cannot be taken as evidence for primary volatile-rich magmas. The characteristic signature of the Black Swan Succession is the presence of highly localised disseminated sulfide within a sequence showing more widespread evidence for crustal contamination and interaction with its immediate substrate. This has important implications for the applicability of trace element geochemistry in exploration for komatiite-hosted nickel deposits.Electronic Supplementary Material Supplementary material is available in the online version of this article at Editorial handling: Peter Lightfoot 相似文献
13.
The use of mineral deposit density regression models to estimate the number of undiscovered deposits is gaining acceptance in mineral resources assessments. The deposit density regression models currently in use are based on well-established power law relationships between deposit density (deposits/km2) and the areal extent of the host rocks in well explored regions (control areas) worldwide. Although these generalized or global deposit density models can generate guideline estimates that are useful at the terrane scale, locally-derived terrane-based deposit density regression models may potentially yield more relevant estimates at the terrane scale. Using 12 selected komatiite-defined control areas in the Kalgoorlie Terrane, Western Australia, we found that the size (km2) of the control areas had power law relationships with (i) nickel sulphide deposit density, and (ii) nickel endowment density (nickel metal/km2). Regression analyses showed that both power law relationships are statistically significant at the 5% level. This suggests that nickel sulphide deposit and endowment density models could be used to estimate the number of undiscovered nickel sulphide deposits and amount of nickel metal endowment in less explored komatiites in the Kalgoorlie Terrane. This study shows that global geological relationships can be viably downscaled onto local geological terranes thereby supporting the hypothesis that the processes of mineral deposit formation and preservation are scale-independent and self-similar. 相似文献
14.
大平掌矿床是西南三江地区重要的铜金多金属矿床，为系统地对比研究矿区16号勘探线新发现两类金矿体，即V1块状硫化物矿体中顺层产出的层状金矿体、穿层断裂带中的网脉状金矿体中金的赋存状态、载金矿物类型，探讨金的沉淀机制。文章基于详实的野外地质调查，运用光学显微镜、扫描电镜(SEM)观察，结合电子探针(EPMA)分析和激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)原位微量元素分析。结果表明，两类金矿体矿石中可见金为金的独立矿物(银金矿、碲金矿、碲金银矿)，以裂隙金形式赋存，层状金矿体矿石中还可见晶隙金；热液型黄铁矿是两类金矿体矿石的主要载金矿物，其中“不可见金”均以固溶体金(Au+)为主，存在极少数的纳米金(Au0)。两类金矿体金的成矿均受后期东西向断裂带影响，为后期具有较高碲逸度的成矿热液充填成矿提供有利空间，金的独立矿物颗粒细小且分布不均，是由流体的沸腾和混合作用以及不平衡、不稳定的流体体系造成；两类金矿体中固溶体金(Au+)均由Au+占据黄铁矿晶格空位或缺陷等畸变形成。 相似文献
15.
西天山阿希浅成低温热液金矿床剥蚀改造过程探讨 总被引：1，自引：0，他引：1
阿希金矿床是新疆西天山成矿带上与晚古生代火山岩有关的典型浅成低温热液型金矿床。矿区包括热液成因和沉积成因2种类型的金矿体。其中,热液成因金矿体明显受近南北向断裂控制,并遭受一定的剥蚀改造,矿体空间形态变化特征及黄铁矿热电性标型特征显示矿床南段比北段剥蚀程度高,矿体金品位和厚度质量参数空间分布特征显示矿体具有向北侧伏特征;沉积底砾岩型金矿体角度不整合于热液成因矿体之上,其含矿砾石类型和稀土元素分布特征与热液型矿体基本一致,为热液型矿体遭受剥蚀并在北东部阿恰勒河组中沉积的产物。基于以上认识,并结合矿床的形成、产状变化特征、区域构造地质演化等资料的深入分析,建立了阿希浅成低温热液型金矿床的剥蚀改造模式。 相似文献
16.
玲珑金矿田矿物组合与地球化学分带及矿体定位预测意义 总被引：9，自引：0，他引：9
详细讨论了玲珑金矿田矿物组合和元素的空间分带，二之间的一致性说明矿物组合的空间分带是宏观的元素地球分带，且具有远程有序和短程无序的特点。同时在矿田水平方向上，由于SE→NW金属矿物的种类和含量呈增加的趋势，由少硫化物蚀变岩型向多金属硫化物石英脉型变化。由于不同矿物组合的矿脉赋矿标高具有较大的差异，这为矿体的定位预测提供了矿物学依据；另外矿物组合的垂向分带，对判定矿体的剥蚀深度和延深也具有重要的参考价值。 相似文献
17.
澳大利亚西部伊尔岗克拉通卡尔古利地体是世界上太古宙与科马提岩有关的硫化物镍矿床最为集中的地区。该区科马提岩型硫化镍矿床主要有两大类型：①由高品位的块状、海面陨铁状和网状矿石组成,赋存于科马提岩熔岩流（主要为火山橄榄岩）底部,以卡姆巴尔达矿床为代表;②以低品位的浸染状镍硫化物矿石为主,赋存于厚层纯橄榄岩的中部,以芒特基斯为代表。与镍成矿有关的科马提岩形成于晚太古代（2．70Ga）,具铝不亏损（Al2O3／TiO2=15～25）地球化学特征,一般形成于具含硫围岩的动态高岩浆流环境。伊尔岗克拉通科马提岩型镍硫化物矿床形成于经历岩浆作用（结晶、分异和浓集）和地壳硫混染作用的硫不饱和镁铁质-超镁铁质岩浆的熔岩通道或管道中。在矿床成因讨论的基础上,提出该类型矿床的找矿标志和勘查方法。 相似文献
18.
Komatiites and nickel sulfide ores of the Black Swan area,Yilgarn Craton,Western Australia. 2: Geology and genesis of the orebodies 总被引：1，自引：0，他引：1
The Black Swan Ultramafic Succession hosts a number of magmatic Fe–Ni–Cu–PGE sulfide ore shoots, ranging from high grade massive ore to low grade disseminated sulfides. Of these, the most economically significant is the Silver Swan massive sulfide orebody, associated with the basal contact of the succession. The deposit varies in thickness between 5 and 20 m, reaches a N–S strike length of 75 m, extends for at least 1.2 km of vertical plunge and is open at depth. Overlying matrix (net-textured) ore is rare. Inclusions of dacite are abundant within the lower 5 m of the massive sulfide. They range from angular fragments through smooth sinuous and plumose morphologies to fine lace-like intergrowths with the sulfide matrix, and comprise variable proportions of cores of porphyritic dacite and carapaces with skeletal plagioclase phenocrysts. Dynamic crystallisation and kinetic melting textures in the carapaces indicate that the inclusions have been heated to various temperatures, some well above their liquidus temperature. The composition of the inclusions ranges from a perfect match with the immediate footwall dacites to mixtures of dacite with up to 30% komatiite. The consistent thickness of the inclusion-bearing basal layer within the massive sulphide is interpreted as the extent of 3-D physical connectivity between the inclusions and a partially molten underlying hybrid layer. Primary contacts between the Silver Swan massive sulfide orebody and overlying ultramafic rocks are marked by thin rinds containing coarse-grained chevron-textured chromites with skeletal textures. Compositions of these chromites match those from Kambalda, Perseverance and other localities, and are inconsistent with a metamorphic origin. They are interpreted as markers of primary magmatic contacts. The combination of this feature with the general paucity of matrix ore implies that the massive ore accumulated and solidified before the accumulation of the overlying thick sequence of olivine cumulates. Taken together with observations on the internal fractionation of platinum group elements within the massive ores, these observations are consistent with a model where the massive ore were emplaced at the floor of a small partially drained lava tube. The floor of the tube had been previously heated by passage of large volumes of lava, such that it had reached its melting range. The felsic inclusions within the ore are the result of buoyant ascent of partially molten substrate into the ore magma. This constitutes strong evidence for the operation of thermo-mechanical erosion during ore emplacement. The disseminated Cygnet and Black Swan orebodies show a number of distinctive features. Cygnet contains a assemblage of clasts and inclusions which are interpreted as the result of rip-up, transport and redeposition of sulfides from a pre-existing massive sulfide orebody, of which Black Duck may be a remnant. The Black Swan orebody, by contrast, does not show xenolithic features, but is characterised by an association of sulfide blebs with segregation vesicles, and by unusually coarse-grained olivine. The Black Swan orebody is interpreted as the result of transport of sulfide droplets within a lava charged with a suspended load of coarse olivine crystals.Editorial handling: Peter Lightfoot 相似文献
19.
产于金沙江结合带与维西晚古生代-早中生代火山弧交接部位加仁岩体北倾覆端羊拉铜矿,含矿岩系为泥盆系江边组和里农组,属一套火山岩、砂泥质硅质复理石建造,是火山-喷流沉积作用产物,形成(似)层状块状硫化物矿体;中-晚印支期中酸性岩侵入对原生层状矿体进行了叠加,形成了矽卡岩富厚矿体,里农矿段KT1和KT5层状矿体在产状、规模、分带性和矿物组构等方面与传统接触交代矽卡岩存在显著差异,并从矿物学、地球化学特征显示具明显同生矿化后期叠加改造特征,该期也可单独形成矽卡岩型矿体,及由钙铁榴石、钙铁辉石、阳起石、绿帘石等组成无矿化矽卡岩;晚印支-早燕山期形成NE向大脉状矿体,部分小型脉状斑岩型矿体。显示主要为三期叠加型矿床,是金沙江洋及其邻区构造演化在矿区的集中体现。根据矿体类型、保存条件及围岩性质等进行缺位预测、找矿与勘查。 相似文献
20.
沃溪金锑钨矿床中网状细脉型矿体是一种容易被忽略的有价值的矿体,探明矿石量120万吨。这种矿体赋存于主脉(层状含矿石英脉)间蚀变板岩中,与主脉有着密切的关系,严格受主脉旁的次级构造控制。矿体呈楔状、透镜状、囊状。有白钨矿-自然金、白钨矿-辉锑矿-自然金、单一自然金三种矿化类型。 相似文献