刚果（金）加丹加省KABARE铜钴矿床地质特征及成因分析

KABARE铜钴矿区位于刚果(金)加丹加铜矿带大型推覆构造带的北部.该矿床地质工作及研究程度极低,铜钴矿体受地层、后生逆掩挤压及断裂构造复合控制,尤其在逆掩断层带中,罗安群和恩古巴群接触带附近的碎裂岩带,形成蚀变明显的铜钴赋矿岩性组合.通过区域地质背景、矿床地质特征分析,认为该矿床经历了早期成岩成矿阶段,后期多期构造热液叠加富集,晚期次生氧化及表生风化淋滤改造多个阶段,为层状多因复控型氧化矿床,受岩性-构造复合叠加控制明显.     

Reviews

The origin of granite

The Granite Controversy, by H. H. Read, xix + 430 pp. Thomas Murby & Co., London, 1957.

Geology of the Pleistocene

Glacial and Pleistocene Geology by R. F. Flint, xiii‐553 pp., 4 pis., figs., J. Wiley & Sons Inc. New York; Chapman & Hall Ltd., London, 1957, 4 plates and numerous figures. $12.50.     

Tertiary stratigraphy of Western Australia

This paper is a summary of the present knowledge of the Tertiary stratigraphy of Western Australia. Also included is new information on the Cainozoic of the Carnarvon Basin, a result of petroleum exploration in the area.

Tertiary rocks formed during more than one cycle of deposition in three basins (Eucla, Perth, and Carnarvon), and also as thin units deposited in a single transgression along the south coast. The Tertiary stratigraphy of the Bonaparte Gulf Basin is not well known.

Drilling in the Eucla Basin has encountered up to 400 m of Tertiary in the south central part, with uniform thinning towards the margins. The section begins with a middle‐upper Eocene carbonate unit which represents the dominant event in the Tertiary sedimentation in this basin. More carbonates were deposited in the late Oligocene‐early Miocene and middle Miocene.

Along the south coast, the so‐called Bremer Basin, the Plantagenet Group (up to 100 m) of siltstone, sandstone, spongolite, and minor limestone, was deposited during the late Eocene.

The Perth Basin contains up to 700 m of Tertiary sediment, formed during at least two phases of sedimentation. The upper Paleocene‐lower Eocene Kings Park Formation consists of marine shale, sandstone, and minor limestone, with a thickness of up to 450 m. The Stark Bay Formation (200 m) includes limestone, dolomite, and chert formed during the early and middle Miocene. Events after deposition of the Stark Bay Formation are not well known.

The northern Carnarvon Basin and Northwest Shelf contain by far the most voluminous Tertiary sediment known from Western Australia: 3500 m is known from BOCAL's Scott Reef No. 1. A more usual maximum thickness is 2500 m. Most sediments were laid down in four episodes, separated by unconformities: late Paleocene‐early Eocene; middle‐late Eocene; late Oligocene‐middle Miocene; and late Miocene to Recent.

The Paleocene‐early Eocene cycle consists of about 100–200 m (up to 450 m in the north) of carbonate, shale, and marl of the Cardabia Group containing rich faunas of planktonic foraminifera.

The middle‐late Eocene sediments include diverse rock types. Marine and nonmarine sandstone formed in the Merlinleigh Trough. At the same time, the Giralia Calcarenite (fauna dominated by the large foraminifer Discocyclina) and unnamed, deeper water shale, marl, and carbonate (with rich planktonic foraminiferal faunas) formed in the ocean outside the embayment. Thickness is usually of the order of 100–200 m.

The main cycle of sedimentation is the late Oligocene‐middle Miocene, during which time the Cape Range Group of carbonates formed. This contains dominantly large foraminiferal faunas, of a wide variety of shallow‐water microfacies, but recent oil exploration farther offshore has recovered outer continental shelf facies with abundant planktonic foraminifera. A minor disconformity representing N7 and perhaps parts of N6 and N8 is now thought to be widespread within the Cape Range Group. The last part of this cycle resulted in sedimentation mainly of coarse calcareous marine sandstone (unnamed), and, in the Cape Range area, of the sandstone and calcareous conglomerate of the Pilgramunna Formation. Maximum thickness encountered in WAPET wells is 900 m.

After an unconformity representing almost all the late Miocene, sedimentation began again, forming an upper Miocene‐Recent carbonate unit which includes some excellent planktonic faunas. Thickness is up to 1100 m.

Thin marine sediments of the White Mountain Formation outcrop in the Bonaparte Gulf Basin. They contain some foraminifera and a Miocene age has been suggested.     

Chemical fingerprinting of multiple large-scale magmatic events in the Mesoproterozoic Bangemall Supergroup,Western Australia

Three major igneous events, dated at ～1465, ～1070 and ～500 Ma, are represented in the Proterozoic of central Western Australia, yet their extent is poorly understood. The compositions of dated mafic rocks from the western Bangemall Supergroup of Western Australia have been used to establish a chemical fingerprint for the ～1465 Ma and ～1070 Ma intrusive events, and to assign sills of an unknown age to one of the two events. A similar approach has been used to identify the extent of ～500 Ma magmatism. Low-pressure fractionation or accumulation has exerted a strong influence on the chemistry of rocks from all magmatic events, but distinctive trace-element ratios (e.g. Th/Nb, Nb/Zr) and rare-earth element (REE) chemistry (e.g. Eu/Eu?, (Gd/Yb)_CN) can discriminate different events. These ratios remain constant regardless of the degree of fractionation or accumulation, and reflect the chemistry of the respective mantle sources. Based on chemistry, ～500 Ma igneous rocks are not found in the Bangemall Supergroup. Neodymium model ages for ～1465 Ma sills overlap with crystallisation ages of subduction-related felsic intrusive rocks from the adjacent Gascoyne Complex, and this, combined with trace-element and REE chemistry, suggests that the mantle source for these sills underwent ～5% crustal contamination approximately 450 Ma prior to melting in a subduction zone environment. Unrealistically large amounts of contaminant are required to explain the chemistry of most ～1070 Ma sills, and their chemistry is better explained by melting of a heterogeneous mantle source, consistent with the overlap of Nd model ages and crystallisation ages. However, the relatively low εNd(T) and high ⁸⁷Sr/⁸⁶Sr(T), elevated light REE, Rb and Zr concentrations, and high Th/Nb of some ～1070 Ma eastern Bangemall Supergroup sills are indicative of crustal contamination. These sills are relatively depleted in chalcophile elements and platinum-group elements, consistent with coeval precipitation of sulfides and crustal contamination. The overlap in the maximum depositional age of host-rocks with the crystallisation age of some sills, the confining of most ～1465 Ma sills to older parts of the stratigraphy, and field evidence showing that some sills belonging to both the ～1465 and ～1070 Ma events were intruded into wet sediments, indicate a close temporal relationship between sedimentation and sill intrusion.     

Reaction relationships during retrograde metamorphism at Olary, South Australia

Abstract In metapelitic schists of the north-eastern Weekeroo Inliers, Olary Block, Willyama Supergroup, South Australia, syn-S1 and syn-S2 assemblages involving staurolite, garnet, biotite and another mineral, most probably cordierite, were overgrown by large syn-S3 andalusite porphyroblasts, owing to isobaric heating from metamorphic conditions that existed during the development of S2. Conditions during the development of S3 probably just reached the andalusite—sillimanite transition. During the development of S4, at somewhat lower temperatures than those that accompanied the development of S3, the following reaction occurred:
staurolite + chlorite + muscovite ± biotite + andalusite + quartz + H₂O.
The amount of retrogression is controlled primarily by the amount of H₂O added by infiltration. As the syn-S3 matrix assemblage was stable during the development of S4, but the andalusite porphyroblasts were no longer stable with the matrix when H₂O was added, the retrogression is focused in and around the porphyroblasts. With enough H₂O available, and if quartz was consumed before biotite in a porphyroblast, then the following reaction occurred:
staurolite + chlorite + muscovite + corundum ± biotite + andalusite + H₂O.
This reaction allowed corundum inclusions in the andalusite to grow, regardless of the presence of quartz in the matrix assemblage.     

Palaeobiology of Mesoproterozoic Salkhan Limestone, Semri Group, Rohtas, Bihar, India: Systematics and significance

Mesoproterozoic (∼ 1600 Ma old) Salkhan Limestone (Semri Group) of the Vindhyan Supergroup, exposed in Rohtas district of Bihar, India, preserves an abundant and varied ancient microbial assemblage. These microfossils are recorded in three distinctly occurring cherts viz., bedded chert, stromatolitic chert and cherty stromatolites. 27 morphoforms belonging to 14 genera and 21 species have been recognized. Six unnamed forms are also described. The microbial assemblage, almost exclusively composed of the remnants of cyanobacteria, is dominated by entophysalidacean members and short trichomes and can be termed as ‘typical Mesoproterozoic microbiotas’. The assemblage includes characteristic mat-forming scytonematacean and entophysalidacean cyanobacteria.Eoentophysalis is the dominant organism in the assemblage. Ellipsoidal akinetes of nostocalean cyanobacteria(Archaeollipsoides) and spherical unicells also occur; both are distinct from mat forming assemblage, allochthonous and possibly planktic. Co-occurrence of the microbiotas and precipitates is related to the depositional environment of the Mesoproterozoic tidal flats with high carbonate saturation.     

Crystal Size Distribution (CSD) and Textural Evolution of Accessory Apatite, Titanite and Allanite during Four Stages of Metamorphism: an Example from the Moine Supergroup, Scotland

Crystal size distributions (CSD) and shapes of accessory apatite,titanite and allanite are investigated in three texturally distinctgarnet zones (Z1–Z3) and in the matrix (Z4) of a garnet–epidote–biotitegneiss from the Moine Supergroup. Additionally, textural relationshipsand interactions between the accessory minerals and surroundingrock-forming minerals are considered, results of numerical CSDmodelling are presented, and geochronological and geologicalconsequences of the inferred CSD evolutions are discussed. Texturesand CSDs indicate that the accessory minerals were in, or near,a stage of nucleation and initial growth immediately prior togarnet Z1 overgrowth, and formed within less than 20 000 years,either by a size-independent or size-dependent growth mechanism.Subsequently, the CSDs were modified by different growth mechanisms,as supported by several parameters including CSDs, grain numbers,grain sizes, specific volumes and others. The apatite CSD evolutionfrom Z1 to Z4 is consistent with open-system LPE (Law of ProportionateEffects) growth accompanied and followed by supply controlledrandom ripening, whereas transformation of the original titaniteCSD is more consistent with Ostwald ripening, temporarily accompaniedby positive or negative McCabe growth. The allanite CSDs alsopoint to Ostwald ripening between Z3 and Z4. The textural observationsindicate that the growth evolution of the accessory phases wasinfluenced by mineral reactions with surrounding rock-formingminerals, as well as by deformation and matrix coarsening, ina manner similar to that found in more simple ceramic systems.The observed textures require a successive temperature risethroughout the tectono-metamorphic evolution of the investigatedrock, in agreement with existing P–T data. Fast nucleationand initial growth of the accessory minerals during Z1 was perhapsinitiated by contact metamorphism, whereas subsequent growthand annealing (Z2–Z4) result from regional metamorphicevents. KEY WORDS: apatite; titanite; allanite; CSD; Moine Supergroup; textures; kinetics     

刚果(金)加丹加鲁苏西铜钴矿床S、C、O、Sr同位素特征及矿床成因

鲁苏西铜钴矿床位于刚果(金)加丹加铜钴矿带,是该区域典型层控铜钴矿床。该矿床的矿石类型依据氧化程度可分为硫化矿和氧化矿。野外地质观察和区域资料分析表明,硫化矿的成矿期可分为成岩早期和造山期,矿石矿物为黄铜矿、斑铜矿、硫铜钴矿和辉铜矿。氧化矿主要为铜钴硫化物在富水表生环境下淋滤而成。矿床的同位素数据分析表明:该矿床成岩期的硫化物为以生物还原作用为主,硫源来自元古宙海水,碳源以海相无机碳为主,放射性锶同位素与基底物质有关;造山期硫化物生成以热化学还原作用为主,成矿流体来自蒸发盐的溶解,硫源来自早期硫化物再活化和蒸发盐溶解,碳氧同位素表明成矿流体与围岩发生了强烈的缓冲反应。综合分析表明,蒸发相的海水为鲁苏西铜钴矿富集和成岩早期成矿提供了有利条件,造山期改造和表生期氧化对矿床品位的富集影响明显。     

刚果(金)加丹加省遥感地质解译与矿产勘查战略选区

为研究刚果(金)加丹加省内成矿特征和矿床分布规律,以Landsat ETM+为主要信息源,分析了加丹加省遥感影像特征,对其地层、岩体、构造等进行了遥感地质解译,将研究区划分出西部桑多阿—卡尼亚玛构造稳定区、中部北东向构造带影像区、东北部普韦托—卡莱米影像区、东南部卢菲利前陆影像区和南部卢菲利弧形构造带影像区等5个构造影像单元。分析总结了每个构造影像区的主要构造类型、成矿特征、控矿要素及各构造影像区区域应力特征,建立了加丹加省区域构造格架,厘定了各影像区内控岩、控矿大断裂,基本查明了研究区成矿地质背景。在此基础上,结合相关地质矿产资料,筛选出莫坎博铜矿预测区、穆梅纳铅锌矿预测区、Mobambi铜钴矿床预测区、勘苏祁铜钴矿床预测区、Mudinga铜银矿床预测区、Kavabala铜矿预测区及昆圭铜矿预测区等7处有利成矿地段。