澳大利亚西澳州2004-2005年度矿产勘探综述

介绍了澳大利亚西澳州2004—2005年度金、镍、铁、钛、锆、金刚石矿床的勘探情况和取得的找矿成果。简述了2004—2005年度西澳州矿产勘探(包括石油勘探)消费支出、不同矿产品所占勘探支出的份额、钻探、矿山土地复垦及环境保护的情况。     

Alteration zoning and primary geochemical dispersion at the Bronzewing lode-gold deposit, Western Australia

The Late Archaean Bronzewing lode-gold deposit is in the Yandal greenstone belt, Western Australia. It is located in a 500-m-wide, N–S trending, structural corridor consisting of an anastomosing set of brittle–ductile shear zones and is chiefly hosted by tholeiitic basalts, which are metamorphosed at mid- to upper-greenschist facies. Syn-peak metamorphic alteration surround all ore bodies, and alteration extends laterally for ≤80 m from individual mineralised structures. Individual alteration haloes partially overlap and form a >1.5-km-long and ≤300-m-wide domain. The alteration sequence, studied here at 140 m below the present undisturbed surface, comprises distal calcite–chlorite–albite–quartz, intermediate calcite–dolomite–chlorite–muscovite–albite–quartz and proximal ankerite–dolomite–muscovite–albite–quartz–pyrite zones. Mass transfer calculations indicate that chemical changes during alteration include enrichment of Ag, Au, Ba, Bi, CO₂, K, Rb, S, Sb, Te and W, and depletion of Na, Sr and Y. The elements Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, P, Ti, V, Zn and Zr are immobile. The degree of chemical change increases with proximity to gold ore zones. In addition, abundant quartz veins indicate substantial silica mobility during the hydrothermal event, although there is no large relative silica loss or gain in the host rock. The broadest anomaly surrounding the Bronzewing gold deposit is defined by tellurium (>10 ppb) which, if it is a hydrothermal anomaly, extends beyond the 400 × 600 m study area. Anomalous values for CO₂, K, Rb and Sb also define wider zones than does anomalous gold (>4 ppb), although even the lithogeochemical gold anomaly extends across strike for as much as 80 m away from ore and >600 m along the N–S strike of the shear zone corridor. Also carbonation and sericitisation indices outline large exploration targets at the Bronzewing deposit. Sericitisation indices define anomalies that extend for tens of metres beyond visible potassic alteration, whereas the anomalies defined by the carbonation indices do not extend beyond visible carbonation. None of the individual alteration indices or pathfinder elements are able to define consistent gradients towards ore. However, the respective dimensions of individual geochemical anomalies can be used as an extensive, although stepwise, vector towards ore. This sequence is, from species with broadest dispersion first, as follows: Te > CO₂/Ca ≥ Sb, 3K/Al, Rb/Ti ≥ Au, W > Y/Ti (depletion) > Ag ≥ Bronzewing ore. Received: 25 October 1999 / Accepted: 11 May 2000     

Alteration and primary geochemical dispersion associated with the Bulletin lode-gold deposit, Wiluna, Western Australia

The Bulletin lode-gold deposit is within the northernmost part of the Norseman–Wiluna greenstone belt in the Archaean Yilgarn Block, Western Australia. It is located within a brittle–ductile shear zone and hosted by tholeiitic metavolcanic rocks. Syn-metamorphic wallrock alteration envelops the gold mineralisation and is pervasive throughout the entire shear zone and extends up to 150 m into the undeformed wallrocks. Alteration is characterised by the sequence of distal chlorite–calcite, intermediate calcite–dolomite, outer proximal sericite and inner proximal dolomite–sericite zones. The thickness of the alteration envelope, and the occurrence of dolomite in the alteration sequence, can be used as a rough guide to the width, extent and grade of gold mineralisation, because a positive correlation exists between these variables. Mass transfer evaluations indicate that chemical changes related to the wallrock alteration are similar in all host rocks: in general, Ag, As, Au, Ba, CO₂, K, Rb, S, Sb, Te and W are enriched, Na and Y are depleted, and Al, Cr, Cu, Fe, Mg, Mn, Nb, Ni, P, Se, V, Zn and Zr are immobile, while Ca, Si and Sr show only minor or negligible relative changes. The degree of mobility of each component increases with proximity to gold mineralisation. The largest potential exploration targets are possibly defined by regional As (>6 ppm) and Sb (>0.6 ppm) anomalies. These anomalies, if real, extend laterally for >150 m from the mineralised shear zone into areas of apparently unaltered rocks. Anomalies defined by Te (>10 ppb), W (>0.6 ppm), carbonation indices, local enrichment of Sb (>2.0 ppm) and As (>28 ppm), and potassic alteration indices also form significant exploration targets extending beyond the HJB shear zone and the Au anomaly (>6 ppb) and, locally, into apparently unaltered rock. Gold, itself, has a restricted dispersion, with an anomaly extending for 1–35 m from ore, and being restricted to within the shear zone itself. Amongst individual geochemical parameters, only As and Sb define significant, consistent and smooth trends (vectors) when laterally approaching the ore. However, the respective dimensions of individual geochemical anomalies can be used as an extensive, though stepwise, vector towards ore.     

The mineral chemistry,near-infrared,and mid-infrared reflectance spectroscopy of phengite from the Olympic Dam IOCG deposit,South Australia

Phengite is the main potassic dioctahedral mica identified at the Olympic Dam iron oxide–copper–gold (IOCG) deposit, South Australia, where its mineral chemistry is quite variable. These differences can be explained by contrasting degrees of hydrothermal alteration. In the heavily-sericitized, ore-bearing rocks, the phengites display a lower-Si content, a higher-Al content, and a lower Mg-number than the phengites from the weakly-sericitized alteration halo that surrounds the deposit. Variations are also observed in the near- and mid-infrared reflectance spectra collected from phengite-bearing rocks. In the near-infrared, high-Al phengite produces a spectral absorption feature at 2.206 μm, and this feature is displaced to 2.213 μm for low-Al phengite. In the mid-infrared, high-Al phengite produces a strong reflectance peak at 9.59 μm, whereas this peak is observed at 9.57 μm in the spectra from low-Al phengite. Additional peaks were also identified at 10.98, 12.22, and 13.33 μm. These were most intense in the spectra from high-Al phengite. A drill core profile was produced using the results of the spectral analysis that shows the change in phengite mineral chemistry and phengite abundance as a function of depth. In general, near- and mid-infrared reflectance spectroscopy can be used to characterize the aluminum content of potassic dioctahedral micas like phengite, and this information can be used to infer the degree of sericitic alteration that has occurred as a result of hydrothermal fluid flow.     

The Mesoproterozoic Abra polymetallic sedimentary rock-hosted mineral deposit,Edmund Basin,Western Australia

Abra is a blind, sedimentary rock-hosted polymetallic Fe–Pb–Zn–Ba–Cu ± Au ± Ag ± Bi ± W deposit, discovered in 1981, located within the easterly trending Jillawarra rift sub-basin of the Mesoproterozoic Edmund Basin, Capricorn Orogen, Western Australia. The Edmund Basin contains a 4–10 km thick succession of siltstone, sandstone, dolomitic siltstone, and stromatolitic dolomite. The age of the Edmund Group is between 1.66 and 1.46 Ga. The Abra polymetallic deposit is hosted in siltstone, dolostone, sandstone and conglomerate of the Irregully and Kiangi Creek Formations, but the mineralised zones do not extend above an erosion surface marking the change from fluvial to marine facies in the lower part of the Kiangi Creek Formation. The Abra deposit is characterised by a funnel-shaped brecciated zone, interpreted as a feeder pipe, overlain by stratiform–stratabound mineralisation. The stratiform–stratabound mineralisation includes a Red Zone and an underlying Black Zone. The Red Zone is characterised by banded jaspilite, hematite, galena, pyrite, quartz, barite, and siderite. The jaspilite and hematite cause the predominant red colouration. The Black Zone consists of veins and rhythmically banded sulphides, laminated and/or brecciated hematite, magnetite, Fe-rich carbonate and scheelite. In both zones, laminations and bands of sulphide minerals, Fe oxides, barite and quartz commonly exhibit colloform textures. The feeder pipe (Stringer Zone) merges with Black Zone and consists of a stockwork of Fe-carbonate-quartz, barite, pyrite, magnetite and chalcopyrite, exhibiting fluidised and/or jigsaw textures.The Abra mineral system is characterised by several overprinting phases of hydrothermal activity, from several stages of brecciation and fluidisation, barite and sulphide veining to barren low-temperature chalcedonic (epithermal regime) veining. Hydrothermal alteration minerals include multi-stage quartz, chlorite, prehnite, Fe-rich carbonate and albite. Albite (Na metasomatism) is an early alteration phase, whereas Fe-rich carbonate is a late phase. Fluid inclusion studies indicate that the ore fluids had temperatures ranging from 162 to 250 °C, with salinities ranging from 5.8 to about 20 wt.% NaCl. In the course of our studies, microthermometric and Raman microprobe analyses were performed on fluid inclusions in carbonate, quartz and barite grains. Fluid inclusions in quartz show homogenisation temperatures ranging from 150 to 170 °C with calculated salinities of between 3.7 and 13.8 wt.% NaCl.The sulphur isotopic system shows δ³⁴S values ranging from 19.4 to 26.6‰ for sulphides and from 37.4 to 41.9‰ for barite (Vogt and Stumpfl, 1987, Austen, 2007). Sulphur isotope thermometry between sulphides and sulphide–barite pairs yields values ranging from 219 to 336 °C (Austen, 2007).Galena samples were analysed for Pb isotope ratios, which have been compared with previous Pb isotopic data. The new Pb isotope systematics show model ages of 1650–1628 Ma, consistent with the formation of the host Edmund Basin.Re–Os dating of euhedral pyrite from the Black Zone yielded an age of ~ 1255 Ma. This age corresponds to the 1320–1170 Ma Mutherbukin tectonic event in the Gascoyne Complex. This event is manifested primarily along a WNW-trending structural corridor of amphibolite facies rocks, about 250 km to the northwest of the Abra area. It is possible that the Re–Os age represents a younger re-activation event of an earlier SEDEX style system with a possible age range of 1640–1590 Ma.A genetic model for Abra is proposed based on the above data. The model involves two end-members ore-forming stages: the first is the formation of the SEDEX style mineral systems, followed by a second multi-phase stage during which there was repeated re-working of the mineral system, guided by seismic activity along major regional faults.     

贵州竹林沟锗锌矿床碳酸盐矿物学和矿物化学特征及其地质意义

以碳酸盐岩为容矿岩石的后生热液铅锌矿床（Mississippi Valley-type,MVT矿床）是世界上一种重要的铅锌矿床类型,也是锗的重要工业来源之一。热液碳酸盐矿物是MVT矿床中最主要的脉石矿物,其形成贯穿整个MVT矿床成矿过程。因此,碳酸盐矿物携带丰富的成矿信息,是认识MVT矿床成因的重要补充。位于贵州省贵定县境内的竹林沟锗锌矿床,是近年来新发现的富锗锌矿床（平均品位97.9×10^-6 Ge,6.54% Zn）,赋存于泥盆系碳酸盐岩中。本次工作发现该矿床不同期次热液白云石的矿物学和微量元素地球化学特征存在明显差异：成矿期前白云石（Dol1）主要呈细脉状穿插围岩,被成矿期白云石和硫化物脉穿插,部分呈细粒状被后期白云石包裹;成矿早期白云石（Dol2）主要呈粗粒状,与闪锌矿共生;主成矿期白云石（Dol3）主要呈脉状、团块状,与闪锌矿和黄铁矿共生;成矿晚期白云石（Dol4）呈团块状充填于闪锌矿矿石或者围岩中;成矿期后白云石（Dol5）呈脉状穿插或包裹其它期次白云石/闪锌矿-黄铁矿条带。C-O同位素研究表明,成矿期白云石主要来源于碳酸盐围岩的溶解,成矿流体中的C来源于围岩,而较低的δ¹⁸O值可能是亏损¹⁸O的成矿流体和围岩间水/岩反应过程中O同位素发生交换的结果。激光剥蚀电感耦合等离子体质谱（LA-ICPMS）白云石原位微量元素分析结果表明,Dol2-Dol4的Y/Ho比值相对稳定（30.5~47.9）,结合区域成矿特征,认为形成成矿期白云石的流体主要为盆地卤水,与该矿床属于MVT矿床事实吻合。Dol1和Dol5具有相对较低的稀土总量（∑REE=3.97×10^-6~29.7×10^-6）,很可能与白云岩围岩（∑REE=25.2×10^-6~61.3×10^-6）溶解作用有关,直接继承围岩的稀土元素组成特征;成矿期Dol2-Dol4的∑REE较高（∑REE=39.2×10^-6~117×10^-6）,暗示成矿流体本身也携带了部分稀土元素。成矿各期次白云石均具有明显的Eu负异常（δEu=0.38~0.72）特征,指示成矿温度可能较高（>200℃）,Ce正异常相对稳定（δCe=1.10~1.28）,暗示其成矿流体pH值保持弱酸性。综上,本文认为竹林沟锗锌矿床的形成经历如下过程：在伸展背景下,深循环盆地卤水萃取下伏地层和基底岩石中的Zn、Ge和REE等元素,形成富金属流体,受构造作用驱动沿区域性断裂不断向上运移,在赋矿层位与富硫流体发生混合作用,导致闪锌矿等硫化物沉淀;在整个成矿过程,成矿环境经历了还原→氧化的转变,成矿元素发生了共生分异,在竹林沟形成富锗锌矿体,在牛角塘形成富镉锌矿体,而pH始终保持弱酸性,直至被围岩碳酸盐岩中和。

     

Geochemical exploration for base and precious metal sulphides associated with the Jimberlana Dyke, Western Australia

A geochemical exploration case history is described, dealing with the search for Ni and Cu sulphides, platinoids and chromite associated with the Jimberlana Dyke in Western Australia. The Jimberlana Dyke is a strongly differentiated mafic-ultramafic intrusive exhibiting similarities with the Great Dyke of Rhodesia.Soil sampling was used as the main search technique, the minus 80-mesh fraction of the near-surface soils being analysed for Ni, Cu, Co and Cr by atomic absorption spectrophotometry. Evaluation methods relied initially on visual inspection of element profile plots. Follow-up soil sampling and auger drilling were carried out in anomalous areas to define targets for deeper drill-testing. Subsequent statistical evaluation of the geochemical data has largely confirmed the initial interpretation but has in addition helped to elucidate the excellent correlation existing between the near-surface soil sampling and bedrock geochemistry.The programme was successful in locating a number of occurrences of sulphide mineralization, many of which contained copper and nickel sulphides. The most significant anomaly was at Bronzite Ridge, being related to a small pipe-like body of sulphides with grades up to 2% Ni and 2% Cu. All sulphide intersections tested recorded low values for the platinoid metals. No significant chromite segregations were located and high Cr values in soils (> 1%) can be attributed to a combination of lateritic and eluvial concentration processes.Although no economic mineralization was located the programme demonstrated the extreme sensitivity of Cu as an indicator of sulphides even through moderately thick soil cover.     

应用构造叠加晕在胶东山后金矿找矿的效果

胶东山后金矿位于招平断裂中南段，是一破碎带中低温热液蚀变岩型金矿床，其成矿作用具有多期、多阶段叠加的特点。根据构造叠加晕理论，建立了山后金矿床的构造叠加晕模型，对1-1、1-2号矿体深部进行了找矿预测，认为前者深部矿化较弱，后者矿化较强，并且矿体有较大延深。经工程验证预测结果与钻孔见矿情况基本吻合。     

Trace elements mineral chemistry of sulfides from the Woxi Au-Sb-W deposit,southern China

The Woxi Au-Sb-W deposit is one of the largest polymetallic ore deposits in the Xuefengshan Range, southern China, hosted in low-grade metamorphosed Neoproterozoic volcaniclastic rocks. The orebodies of the deposit are predominantly composed of banded quartz veins, which are strictly controlled by bedding and faults. Petrographic observations and geochemical results are reported on the occurrence of Au and properties of the ore-forming processes for different stages in the deposit. The veins extend vertically up to 2 km without obvious vertical metal zoning. The ore-forming process can be subdivided into four mineralization stages: Pre-ore stage; Early stage (scheelite-quartz stage); Middle stage (pyrite-stibnite-quartz stage); and Late stage (stibnite-quartz sage). Four types of pyrite (Py0, Py1, Py2, and Py3) were identified in the ores and host-rock: Py0 occurs as euhedral grains with voids in the core, ranging in size from 50 to 100 μm and formed mainly in the Pre-ore stage and Early stage; Py1 occurs as subhedral grains. Small grains (around 10 μm) of Py1 form irregularly shaped clusters of variable size ranging from tens to hundreds of μm and mainly formed in the Middle stage; Euhedral-subhedral fine-grained Py2 formed in the Late stage; Minor subhedral fine-grained Py3 was deposited in the Late-stage. Stibnite is widely distributed in the Middle and Late stage ore veins. No systemic difference was recognized in mineralogical features among stibnite formed in different stages. In addition to native gold, the lattice bound Au⁺¹ widely exists in Py1 and Py2 in the deposit, and widespread Py1 is considered as the main Au-bearing mineral with the highest Au contents. Most elements (such as Co, Ni, Cu, As, Sb, Ba, and Pb) are considered to occur as solid solution within the crystal lattice and/or invisible nanoparticles in sulfides minerals. The Co/Ni ratio of most pyrite is lower than 1, suggesting that the metals in the ore-forming fluid are sourced from sedimentary rocks. The coupled behavior between Au and As; Au and Sb suggests that the substitution of As and Sb in pyrite can enhance the incorporation of Au. Variation of trace elements in pyrites of different stages suggests some information on the mineralization processes: Large ion lithophile elements (such as Ba and Pb) are enriched in Py0 indicating that water-rock reaction occurred in the Early stage; Fine-grained Py1 with a heterogeneous distribution of elements suggests fast crystallization of pyrite in the Middle stage.     

Petrology of the Albany and Torbay Adamellite Plutons,near Albany,Western Australia

The Albany and Torbay Adamellites are composite plutons emplaced in Pre‐cambrian gneisses of the Albany‐Esperance Block in the vicinity of Albany, Western Australia. The gneissic country rocks have been metamorphosed to the lower granu‐lite facies at Albany and the upper amphibolite facies at Torbay. Granitized aureoles about 1 km wide, metasomatically enriched in SiO₂, K₂O, and various trace elements commonly including Rb, Ba, La, Pb, and Th, are developed in the gneisses around both plutons. Field relations suggest late‐kinematic magmatic emplacement of the Adamellites in the catazone. Both show chemical variation trends comparable with the trends normally associated with fractional crystallization of calc‐alkali magmas, and their normative compositions correspond with the thermal trough in the system An‐Ab‐Or‐Q‐H₂O at 4–7 kb P_H2o, suggesting an origin involving crystal‐liquid equilibria at a water vapour pressure of about this value. The initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7118 for the Albany Adamellite is consistent with derivation of the magma from crustal rocks. The late‐kinematic field characteristics of the plutons and the limited isotopic data available are compatible with emplacement and crystallization during the closing stages of orogeny and regional metamorphism. The magmas are believed to have been generated not at their present sites of emplacement, but in a deeper, higher‐temperature zone of the crust, with magma generated during an earlier phase of the orogeny.     

铬铁矿自然重砂组合特征及其找矿意义

为探究与基性—超基性岩有关的铬铁矿床所体现的重砂矿物类型及其组合特征,在西藏、新疆、甘肃、青海、内蒙古、河北和陕西7个省（自治区）共选择14个典型铬铁矿床（点）,对所响应的自然重砂矿物进行统计。研究表明,这些矿床（点）中所响应的矿物主要为铬铁矿及铬尖晶石,计算出所涉及重砂矿物的报出频数及报出率,并通过图解直观地表现出与基性—超基性岩有关的铬铁矿床的自然重砂矿物组合,为与基性—超基性岩有关的铬铁矿找矿勘查提供了重要的矿物学依据。     

Primary stratigraphic controls on ore mineral assemblages in the Wannaway komatiite-hosted nickel-sulfide deposit,Kambalda camp,Western Australia

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.     

中蒙边境欧玉陶勒盖大型铜-金矿床的发现及对找矿勘查工作的启示

近年来,随着找矿勘查工作的深入和一批重要铜多金属矿床的发现,中蒙边境已成为21世纪初全球铜、金等矿产找矿勘查的热点地区之一,欧玉陶勒盖铜-金矿床的发现和勘探即是很好的例证。认真分析和研究该矿床的产出大地构造背景,了解矿床产出的地质、岩石学特征,对于中蒙边境中国一侧提高找矿勘探水平具有很好的指导意义。     

Significance of weathering and regolith/landscape evolution for mineral exploration in the NE Albany-Fraser Orogen,Western Australia

The Albany-Fraser Orogen (AFO), southeast Western Australia, is an underexplored, deeply weathered regolith-dominated terrain that has undergone complex weathering associated with various superimposed climatic events. For effective geochemical exploration in the AFO, integrating landscape evolution with mineralogical and geochemical variations of regolith and bedrock provides fundamental understanding of mechanical and hydromorphic dispersion of ore and pathfinder elements associated with the different weathering processes.In the Neale tenement, northeast of the AFO, a residual weathering profile that is 20-55 m thick was developed under warm and humid climatic conditions over undulating Proterozoic sheared granitoids, gneisses, schists and Au-bearing mafic rocks. From the base, the typical weathering profile consists of saprock, lower ferruginous saprolite, upper kaolinitic saprolite and discontinuous silcrete duricrust or its laterally coeval lateritic residuum. These types of duricrusts change laterally into areas of poorly-cemented kaolinitic grits or loose lateritic pisoliths and nodules.Lateritic residuum probably formed on remnant plateaus and was transported mechanically under arid climatic conditions over short distances, filling valleys to the southeast. Erosion of lateritic residuum exposes the underlying saprolite and, together with dilution by aeolian sands, constitutes the transported overburden (2-25 m thick). The reworked lateritic materials cover the preserved silcrete duricrusts in valleys. The lower ferruginous saprolite and lateritic residuum are well developed over mafic and sulphide-bearing bedrocks, where weathering of ferromagnesian minerals and sulphides led to enrichment of Fe, Cu, Ni, Cr, Co, V and Zn in these units. Kaolinitic saprolite and the overlying pedogenic silcrete are best developed over alkali granites and quartzofeldspathic gneisses, which are barren in Au and transition elements, and enriched in silica, alumina, rare earth and high field strength elements.A residual Au anomaly is formed in the lower ferruginous saprolite above a Au -bearing mafic intrusion at the Hercules prospect, south of the Neale tenement, without any expression in the overlying soil (< 20 cm). Conversely, a Au anomaly is recorded in the transported cover, particularly in the uppermost 3 m at the Atlantis prospect, 5 km southwest of the Hercules prospect. No anomalies have been detected in soils using five different size fractions (> 2,000 μm, 2,000-250 μm, 250-53 μm, 53-2 μm and < 2 μm). Therefore, soil cannot be efficiently applied as a reliable sampling medium to target mineralization at the Neale tenement. This is because mechanical weathering was interrupted by seasonal periods of intensive leaching under the present-day surface conditions and/or dilution by recently deposited aeolian sediments which obscure any signature of a potential Au anomaly in soils. Therefore, surface soil sampling should extend deeper than 20 cm to avoid dilution by aeolian sands and seasonal leaching processes. Regolith mapping and the distinction between the residual and transported weathering products are extremely significant to follow the distal or proximal mineralization.     

Mineralogy and Petrology of the Aries Diamondiferous Kimberlite Pipe, Central Kimberley Block, Western Australia

Aries is a deeply weathered micaceous kimberlite pipe (820 Ma)consisting of four lobes: South, Central, North, and North Extension.It is the largest ( 18 ha) and most diamondiferous of the fewkimberlites currently known on the Australian continent, andis rich in country-rock (dolerite and quartzite) xenoliths.Three textural varieties of Aries kimberlites can be recognized,together with autoclastic breccias: (1) macrocrystalmedium-grained;(2) aphanitic (5 vol. % olivine macrocrysts); and (3) macrocrystalsegregated. The kimberlites contain two generations of olivinepseudomorphs (30–40 vol. %), and two of phlogopite (upto 60 vol. %), in a groundmass of apatite, calcite, diopside,sphene, spinels, serpentine, talc, and accessory groundmassminerals including aeschynite [(Ce, Ca) (Ti, Nb)₂O₆], barite,ilmenite, monazite, rutile, siderite, and unidentified Nb-Fe-titanates.Phlogopite zoning is complex and differs from lobe to lobe,but general compositions and trends resemble phlogopites fromkimberlites (TiO₂ 0–5–4 wt. %, A1₂O₃ 9–16%);tetraferriphlogopite substitution is indicated by low Al insome grains. Diopside is low in Cr, Al, Na, and Ti, with highmg-number [molecular Mg/(Mg + Fe²⁺) 93]. Apatite contains upto 17–5% SrO, calcite up to 1–7% SrO but littleMgO or FeO, sphene up to 1.5% Nb₂O₅, and ilmenite 2.6% Nb2O5and 16% MnO but no detectable MgO. Extremely complex moqftiological, textural, and compositionalvariations are present in spinels. They can be divided intofive textural-genetic types: cognate Groundmass chromian spinels(Type G); Inclusions of chromian spinels in olivine macrocrysts(Type I), probably representing either early phenocrysts ormantle xenocrysts: Macrocryst chromian spinels (Type M), probablyrepresenting xenocrysts; late-stage groundmass Fenian spinels(Type F), derived from serpentinization of olivine; Alterationferrian spinels (Type A), found as inclusions associated withsiliceous melt inclusions, in Types I and M, and probably representinginteraction of these earlier types with late-stage melts. Someof these, particularly Types M and F, show further texturalsub-types with no obvious genetic significance. The pipe formed from several magma-pulses. All four lobes maycontain at least one pulse in common, but Central and SouthLobes include additional pulse(s) which yielded distinctivephlogopite zoning, whereas North Lobe and North Extension includepulsc(s) which may have originated at higher mantle levels andyielded more evolved phlogopites. Aries most resembles South African Group II kimberlites mineralogically,certain West African micaceous kimberlites geochemically, andGroup I kimberlites isotopically. A distinctive mantle source-regionis implied by high Nb/U, Ce/Sr, Ce/P, Rb/Ba, and especiallyNb/Zr ratios. Similar anomalous geochemical signatures are sharedwith two other contemporaneous (800 Ma) lampro-phyric intrusionsin the east Kimberley (at Maude Creek and Bow Hill), suggestingthat a scattered alkaline province exists in the Kimberley Block,generated from a regionally anomalous mantle source.     

双频激电法在西澳矿产勘查中的应用

结合双频激电法在西澳大利亚典型覆盖区(热带稀树草原覆盖区)的应用实践,讨论了在特殊地质景观条件下,双频激电法在工作设计中装置选择、工作频率选择、接地电阻改善、电磁耦合克服等方面遇到的问题以及解决这些问题所提出的技术方法,总结整理了一些具有代表性的工作准则和野外工作经验。结论表明:双频激电法在澳洲某金矿的特殊地理环境下的应用效果良好,圈定的激电异常符合地质预期,有进行工程验证的必要;使用双频激电法,在设计及施工过程中应综合分析各方面的影响因素,科学决策,并对可能影响测量数据准确性的因素采取有效的措施,这样才能充分发挥其技术优势,取得令人满意的成果。     

Mineralogy and genesis of the trench tungsten-molybdenum deposit,mount mulgine,Western Australia

The Mount Mulgine Trench deposit is a large, low grade W-Mo resource in Archaean greenstone-granitoid terrain in the Yilgarn Block, Western Australia. The mineralization occupies a quartz vein stockwork zone in a sequence of altered meta-basalts and banded iron formations. The nearby Hill deposit is hosted by a quartzmuscovite greisen on the margin of the synkinematic Mulgine Granite. Fluid inclusion studies show mineralization of the Trench deposit formed over a wide range of temperatures (approximately 500° to 260°C) from a fluid dominated by CaCl₂. Scheelite is the dominant W mineral and fluid inclusion data indicate deposition at temperatures of about 420° to 360°C from a fluid containing about 16 wt% CaCl₂ equivalent. Field relationships and sulphur isotope studies indicate a magmatic hydrothermal origin related to the Mulgine Granite. Fractures formed during intrusion of the granite provided channels for fluid migration and sites for mineral deposition. Controlling factors on mineral deposition may have been the temperature gradient away from the cooling granite and an increase in a _Ca ² resulting from fluid/rock interaction.     

Diamond exploration and regional prospectivity of Western Australia

Pre-1.6 Ga rocks comprise around 45% of the onshore area of Western Australia (WA), constituting the West Australian Craton (WAC) (including the Archean Yilgarn and Pilbara Cratons) and the western part of the North Australian Craton (NAC). These areas provide the conditions suitable for diamond formation at depth, and numerous diamondiferous lamproite and kimberlite fields are known. As emplacement ages span close to 2500 Ma, there are significant opportunities for diamond-affinity rocks being present near-surface in much of the State, including amongst Phanerozoic rocks. WA’s size, terrain, infrastructure and climate, mean that many areas remain underexplored. However, continuous diamond exploration since the 1970s has resulted in abundant data. In order to advance future exploration, a comprehensive database of results of diamond exploration sampling (Geological Survey of Western Australia 2018) has been assessed. The Yilgarn and Pilbara Cratons have spinel indicators almost exclusively dominated by chromite (>90% of grains), whereas (Mg,Fe,Ti)-bearing Al-chromites account for more of the indicator spinels in the NAC, up to 50% of grains at the Northern Territory (NT) border. Increasing dominance of Al in chromites is interpreted as a sign of weathering or a shallower source than Al-depleted Mg-chromites. Garnet compositions across the State also correlate with geological subdivisions, with lherzolitic garnets showing more prospective compositions (Ca-depleted) in WAC samples compared to the NAC. WAC samples also show a much broader scatter into strongly diamond-prospective G10 and G10D compositions. Ilmenites from the NAC show Mg-enriched compositions (consistent with kimberlites), over and above those present in NT data. However, ilmenites from the WAC again show the most diamond-prospective trends. Numerous indicator mineral concentrations throughout the State have unknown sources. Due in part to the presence of diamondiferous lamproites, it is cautioned that some accepted indicator mineral criteria do not apply in parts of WA. For example Ca-depleted garnets, Mg-depleted ilmenites and Cr-depleted and Al-absent clinopyroxenes are all sometimes associated with strongly diamondiferous localities. Quantitative prospectivity analysis has also been carried out based on the extent and results of sampling, age of surface rocks relative to ages of diamond-prospective rocks, and the underlying mantle structure. Results show that locations within the NAC and with proximity to WA’s diamond mines score well. However, results point to parts of the WAC being more prospective, consistent with mineral chemical data. Most notable are the Hamersley Basin, Eastern Goldfields Superterrane and the Goodin Inlier of the Yilgarn Craton. Despite prolific diamond exploration, WA is considerably underexplored and the ageing Argyle mine and recent closure of operations at Ellendale warrant a re-evaluation of diamond potential. Results of mineral chemistry and prospectivity analysis make a compelling case for renewed exploration.