世界首例独立碲矿床赋矿围岩的地质地球化学研究

大水沟独立碲矿床的直接赋矿围岩为低绿片岩相变质岩。前人认为其原岩为陆源碎屑岩。通过对该赋矿岩系的地质特征（包括岩相学特征与副矿物组合标型特征）、岩石化学特征、硅同位素地球化学特征和稀土元素地球化学特征（包括元素钪的地球化学特征）的研究，证明其原岩为分异程度较低的幔源拉斑玄武岩，并具有典型岩浆玄武岩的演化趋势。     

STRATIGRAPHY OF PRECAMBRIAN ROCKS OF THE WESTERN SECTION OF THE SANGILEN HIGHLAND (TUVA)

The stratigraphic sequence of the Precambrian complex of the western Sangilen Highlands, Tannu Tuva, include schists, schistose sandstones, fine-gravel conglomerates, micaceous and ferruginous quartzites, graphitic marbles, and gneisses of the Teskhem, Mugur, Balyktyghkem, Chartyss, and Naryn formations, which grade upward into one another without break. Deposits containing Lower Cambrian fossils are also known in the area. The ferruginous quartzites, associated with the upper Mugur, mark the principal boundary in Precambrian sedimentary accumulation and indicate the change from terrigenous sediments to calcareous marine sedimentation.

The degree of metamorphism varies considerably, both horizontally and vertically. Terrigenous deposits correspond to the green-schist facies. Local variations in the metamorphism of calcareous deposits apparently result from the variability of original components. Also important is the superimposed injection metamorphism associated with Proterozoic intrusions. --Editor.     

浙江高岭土矿床中氢氧同位素的研究

浙江省是我国高岭土矿的产地之一,矿床主要集中于浙南火山岩地区。浙南地区广泛分布中生代的中酸性火山碎屑岩、熔岩及浅成侵入岩,构造断裂发育,气候温暖湿润,具有风化或热液作用形成高岭土矿床的有利地质条件。     

湖北均县风化型高岭土中蒙脱石矿物的形成和变化

湖北均县风化淋滤型高岭土矿床赋存在与一定风化母岩岩性相依存的同一时代层位中。矿体产于寒武纪下统（∈₁）和震旦系上统灯影组（Zbdn）之间的平行不整合面上,呈断断续续的含矿带。风化母岩为寒武系下统暗色含硫有机质、硅质页岩,含矿带的下盘岩性为灰白色厚层状白云岩。     

Geochemical and mineralogical study of bauxite deposit of Mainpat Plateau,Surguja District,Central India

Bauxite deposits of Mainpat Plateau Surguja District, India, are composed of kaolinite, gibbsite, goethite, anatase, and bohemite. Quartz and micas are absent in the samples. The presence of boehmite and goethite are evidences of intense weathering during the formation of the bauxite deposits. The Mainpat Plateau is a mesa landform, at an elevation of around 1,060 m from msl in comparison to the general elevation of 580, consisting of Archaeans (granite?gneisses, phyllite, etc.) at the base, Gondwanas and Deccan basalt, and at the top having a cover of laterite and bauxite. The extremely high values of the chemical index of alteration, and the low values of the alkali metals and alkali earth metals, support an intense weathering origin for the bauxite deposit. There is evidence of deposition in the deposits based on the presence of pisoids in the bauxite samples and the composition of the parent rock. Kaolin minerals were first produced by the hydrolytic weathering of aluminous sediments and then gibbsite was formed as early kaolin was desilicated. The bauxite is having high TiO₂ up to 17 %. The Mainpat laterite/bauxite deposits are characterized by having 50?58 % average Al₂O₃ and 10?30 % Fe₂O₃.     

陕西省铝土矿地质特征及成矿规律

陕西省已知铝土矿产地主要分布于陕北的府谷县、渭北的铜川-韩城一带和陕南的西乡、镇巴、南郑地区;已知铝土矿都位于沉积间断面上,受地层层位控制,属滨海-浅海相沉积矿床。陕北和渭北铝土矿主要产于石炭系下统下部本溪组,陕南铝土矿主要产于二叠系上统吴家坪组底部王坡页岩段。成矿的地质构造条件是隆起区边缘。成矿物质来源既有基底碳酸盐岩的溶蚀分解物,也有陆源铝硅酸盐岩的风化分解物。气候条件是有利于使岩石中铝质析出的温暖潮湿条件。时间上有一个较长时间的沉积问断。对成矿有利的地形条件是古地形总体比较平缓,有利于铝硅酸盐风化物在缓慢的搬运过程中充分分解析出Al2O3。     

Grain size and geochemistry of surface sediments in northwestern continental shelf of the South China Sea

Eighty-six surface sediments collected from the northwestern continental shelf of the South China Sea (SCS) were analyzed for grain size distribution, calcium carbonate, organic carbon, and major and trace element compositions to investigate sediment provenance and factors controlling their geochemical composition. Sediments from the eastern continental shelf of Hainan Island have higher sand and lower clay content, while the samples from the nearshore Hainan Island have higher contents of gravel and clay. Calcium carbonate contents in samples show a positive correlation with water depth in northwestern shelf of SCS, suggesting that it is related to biological factors. However, the nearshore sediments have higher contents of organic carbon compared to those of the outer shelf, possibly suggesting that the terrigenous organic matter usually deposited in nearshore environments such as bays and estuaries. Compared with the upper continental crust, the samples have relatively lower contents of SiO₂ and Al₂O₃, higher than those of the Pearl and Red river sediments. The low contents of K₂O and Na₂O in sediments from the northwestern continental shelf are consistent with intense chemical weathering in the river basin due to the seasonally hot and humid climate regime. The sediments mainly consist of three components, including the gravel fraction composed of calcareous debris, the sand fraction composed of quartz, and the silt and clay fractions mainly composed of clay minerals. The content of each component depends on grain size, sediment source, biogenesis, and hydrodynamic conditions, which finally controls the chemical composition of the sediments. The distributions of Co/Al₂O₃, Cr/Al₂O₃, and Zr/Sc ratios for sediments in the northwestern continental shelf suggest that source rocks are mainly composed of felsic rocks rather than mafic rocks. There is a distinct difference in sediment source between eastern and western shelf sediments; the eastern shelf sediments are characterized by high Zr/Sc ratios mainly derived from the Pearl River, while the western shelf sediments have relatively low values of Zr/Sc indicating a main contribution possibly sourced from the Red River Basin. Terrigenous materials from Hainan Island usually influence the geochemistry of sediments deposited in the nearshore area.     

晋北晚古生代煤系高岭岩成因模式研究

本文主要研究了山西北部晚古生代煤系高岭岩的岩石、矿物、地球化学特征,确定了高岭岩的主要富集层位:(1)本溪组底部铝土质高岭岩;(2)太原组煤夹矸高岭岩;(3)山西组煤夹矸高岭岩。从而得到研究区高岭岩源岩一为风化壳化学风化作用产物,一为火山碎屑沉积物的结论。进而分析了不同层位、不同源岩高岭岩的成因模式:正常沉积高岭岩成因模式和火山碎屑成岩转化成因模式。     

黔北及邻区上二叠统底部高岭土矿床地质特征及成因

广泛产于黔北地区的高岭土矿在地理分布上与川南一带的叙永式高岭土矿是连续的(图1),其矿床地质特征也颇相似。该类矿床最早在四川见有报导、开采和利用。1982年关铁麟同志据该矿床地质特征认定其为古风化壳残余矿床,并命名为叙永式高岭土矿床。我队曾在黔北及川南叙永一带开展区调工作,在搜集前人有关资料的基础上,开展了部分普查找矿工作后,据其特征将矿床成因划为风化淋积矿床。     

Accessory Minerals in Phosphorites of the Lesser Karatau as an Indicator of Provenance Composition

Issue of determination of the provenance composition based on accessory minerals in the Lesser Karatau phosphate-bearing basin is considered. Detailed lithological studies revealed six types of phosphate-bearing sections with specific composition and genetic affinity of accessory minerals. Vertical and lateral distributions of these minerals are shown for both individual deposits and the entire paleobasin. Data on the composition, genesis, and distribution of accessory minerals in phosphorites of the Lesser Karatau are used to determine the composition of ancient provenance.     

Refractory- and metallurgical-type chromite ores,Zambales ophiolite,Luzon, Philippines

The Zambales ophiolite is the major source of chromite ore in the Philippines. The chromitites are concordant cumulates and are associated with distinct chromitite-bearing sequences within the mantle peridotites. Refractory and metallurgical chromite deposits are spatially separated and related to different lithologic associations, which crystallized from different parental magmas. — Refractory chromite ores (30–44 wt% Cr₂O₃; 20–30 wt% Al₂O₃) are linked with the peridotite-troctolite-olivine gabbro lineage. Two main types were found: (1) Al-rich refractory ores associated with harzburgites and feldspathic periodotites and (2) more Cr-rich varieties associated with lherzolites. — Metallurgical chromite ores (45–53 wt% Cr₂O₃; 12–18 wt% Al₂O₃) are linked with the peridotite-pyroxenite-norite lineage. Two main types were also found: (1) Cr-rich metallurgical ores associated with orthopyroxenites and (2) more Al-rich varieties related to clinopyroxenites. — The chemical composition of chromite within the deposits varies depending on the chromite/silicate ratios of the ore types and grades continuously into accessory chrome spinels in the wall-rock peridotites. — The geochemistry of accessory chrome spinels in various peridotites and mafic cumulates depends on the mineralogical composition and the stratigraphic position of their host rocks.New address: BEB Erdgas und Erdöl GmbH, Riethorst 12, D-3000 Hannover 51The terms chrome-spinels and chromite are used as follows: 1. Chrome-spinel is only used for those occuring as accessory minerals in various ultramafic and mafic rocks (= accessory chrome-spinels). Their chemical composition has been determined only by microprobe analysis. — 2. Chromite is used for ore and ore deposits (=chromitites); the chemical composition has been determined by wet chemistry (AAS) or by microprobe analysis     

Mineral distribution and provenance of heavy mineral sands (zircon,ilmenite, rutile) deposits from the NW Murray Basin,far western NSW,Australia

Abstract

There is significant economic interest in the Murray Basin of southeastern Australia as it is proving to be a major heavy mineral sands (HMS) province that will be one of Australia’s major source for production of rutile, zircon and ilmenite. The distribution and provenance of HMS resources in the Murray Basin is poorly understood because of its huge size, limited exploration and the complex depositional, structural and weathering mechanisms in their development. In this paper, we focus on the Copi North and Magic deposits some 130–180?km south of Broken Hill, NSW. The heavy mineral assemblages of the Copi North and Magic deposits are very similar, with the main economic minerals being ilmenite, leucoxene, pseudorutile, rutile and zircon. Intensive fracturing and brecciation are identified in many samples and are inferred to have been initially caused by multi-stage deformational processes associated with metamorphism and then further developed through alluvial and eolian transportation. Both deposits are classified as ‘medium sands, symmetrical, mesokurtic and moderately well-sorted’. The majority of economic minerals are of low to medium sphericity and subrounded, along with abundant polished eolian quartz grains. The Copi North deposit has coarser and more poorly sorted sediments with higher HMS grades and magnetics content than the Magic deposit, reflecting a higher energy depositional environment. The main source for the HMS for the Copi North and Magic deposits is largely ascribed to the Broken Hill Block. Previous studies have shown that the Broken Hill orebody underwent substantial sub-aerial weathering over hundreds of millions of years. In addition, the complex metamorphic events experienced by the Broken Hill Block were capable of forming the broad series of minerals identified within the Copi North and Magic deposits. The HMS were believed to have been transported through paleovalleys near the Mulculca Fault in a southeast direction representing a feeder system into the NW Murray Basin. Both deposits feature a relatively linear geometry (roughly parallel to the strike of the paleoshoreline), with high HMS grades, modest tonnages, and coarser sediments when compared to WIM-style offshore deposits. Compared to other strandline HMS deposits of the Murray Basin, they are smaller in size although have similar high grades of 3.7–6.9% THM and similar proportions of the HMS assemblage of ilmenite, leucoxene, rutile and zircon. Deposits of similar size and grade are likely to occur throughout the northern part of the Murray Basin.

1. KEY POINTS

2. Both the Copi North and Magic deposits contain similar mineral assemblages with the provenance of the heavy minerals ascribed to the Broken Hill Block.

3. A relatively high energy inshore environment is inferred for the Copi North deposit while a lower energy environment associated with either a foreshore or backshore environment is inferred for the Magic deposit.

4. Deposits of similar mineralogy, grades and size are likely to occur elsewhere throughout the northern Murray Basin.

     

Mineral deposit formation in Phanerozoic sedimentary basins of north-east Africa: the contribution of weathering

The intra- and epicontinental basins in north-east Africa (Egypt, Sudan) bear ample evidence of weathering processes repeatedly having contributed to the formation of mineral deposits throughout the Phanerozoic.The relict primary weathering mantle of Pan-African basement rocks consists of kaolinitic saprolite, laterite (in places bauxitic) and iron oxide crust. On the continent, the reaccumulation of eroded weathering-derived clay minerals (mainly kaolinite) occurred predominantly in fluvio-lacustrine environments, and floodplain and coastal plain deposits. Iron oxides, delivered from ferricretes, accumulated as oolitic ironstones in continental and marine sediments. Elements leached from weathering profiles accumulated in continental basins forming silcrete and alunite or in the marine environment contributing to the formation of attapulgite/saprolite and phosphorites.The Early Paleozoic Tawiga bauxitic laterite of northern Sudan gives a unique testimony of high latitude lateritic weathering under global greenhouse conditions. It formed in close spatial and temporal vicinity to the Late Ordovician glaciation in north Africa. The record of weathering products is essentially complete for the Late Cretaceous/Early Tertiary. From the continental sources in the south to the marine sinks in the north, an almost complete line of lateritic and laterite-derived deposits of bauxitic kaolin, kaolin, iron oxides and phosphates is well documented.     

Structural-morphological features of kaolinite from clayey rocks subjected to different stages of lithogenesis: Evidence from the Voronezh anteclise

This paper reports the results of precision structural-morphological study of kaolinite from clayey rocks taken in various areas of the Voronezh anteclise subjected to different stages of lithogenesis: primary kaolins of the weathering crust, proluvial-talus and lacustrine secondary kaolins, as well as lacustrine-swampy fireproof and deltaic-lagoonal refractory clays. The clayey material was transported over more than 300 km. The formation of the fireproof and refractory kaolin deposits in the Voronezh anteclise was related to the Devonian and Early Cretaceous stages of the geological evolution of the region. In terms of spatiotemporal and facies features, the studied genetic series of the kaolin clay deposits is unique. It was established that the sequential structural-morphological evolution o kaolinite in the considered deposits was caused by its mechanical disintegration during transport and redeposition. Interrelation between organic and mineral matters in the fireproof clays was revealed for the first time. Experimental studies of the behavior of kaolinite during sequential grinding and heating confirmed the main reasons for its natural degradation. The formation of virtually monomineral kaolin clays was provoked by the “flow-through” diagenesis, which is similar to weathering in trend. Evolution of mineral matter of the considered genetic series in kaolinite clay deposits was accompanied by the increase of δ¹⁸O values and their dispersion. Peculiarities identified in the behavior of kaolinite and related oxygen isotope characteristics of different-aged denudation and redeposition products of the Devonian weathering crust can play an indicator role in studying different stages of the lithogenesis of clayey rocks.     

黔西南水银洞超大型金矿龙潭组赋矿层岩相特征及对金成矿的控制

黔西南地区水银洞超大型金矿床产于上二叠统龙潭组,金异常富集的高品位层状-似层状矿体受特定的不纯碳酸盐岩和有利岩性组合控制。对龙潭组赋矿层及围岩开展系统岩石学对比分析,总结制约龙潭组沉积作用及岩石类型的控制因素,分析龙潭组中高品位金矿体产出特征及其对岩性岩相的选择性规律。结果表明,龙潭组整体为一套浅水三角洲泥炭沼泽与滨岸潮坪泻湖相沉积,以富含有机质为特征,灰岩夹层可能代表不同时期的海侵事件;峨眉山玄武岩浆的喷溢改变吴家坪期沉积古地理格局和龙潭组中陆源碎屑岩的成分,发育与火山活动有关的沉积,矿石中铁白云石可能是火山碎屑物质热蚀变产物;富有机质和玄武质火山碎屑的不纯生物碎屑灰岩是金异常富集形成高品位矿体的重要控制因素。在黔西南地区找寻该类型矿床时应重点评价特定的岩石类型及组合特征。     

Trace elements and REE in the Cevonian clastic complexes of the Magnitogorsk Megazone, Southern Urals

The first data on trace-element geochemistry, REEs included, of the Devonian clastic and volcanosedimentary complexes in the Magnitogorsk Megazone have been obtained with ICP-MS. The correlation links and the character of distribution indicate that many elements, including those readily passing into solutions during weathering, were transferred as mechanical suspensions. Therefore, minerals concentrating these elements were largely preserved, as also were the distribution and concentrations of elements inherent to the source rocks. Both accessory minerals (apatite, zircon, Ti-minerals, and magnetite) and rock-forming minerals (pyroxene, amphibole, biotite, serpentine, chlorite, and plagioclase) were found among mineral concentrators. Clay minerals also seem to have participated in the processes. The typical elements of various complexes were identified. The distribution of trace elements is correlated with the stratigraphic position of rocks and depends on the character of the petrographic provinces.     

Mathematical approach to calculate indices for depositional environments of pelagic-hemipelagic-terrigenous sediments on the basis of metallic element concentrations

Modern marine sediments can be classified into terrigenous, hemipelagic, and pelagic types according to the distances from the land for the sites recovered and in terms of lithological characteristics of sediments. Ancient cherts are the best sedimentary rocks to reconstruct ancient depositional environments and hemipelagic and pelagic cherts can be identified in terms of lithologic and stratigraphic characteristics. However, geochemical characteristics of modern sediments and ancient cherts can discriminate them into these three types. Particularly, the degree of correlation between Fe and Mg in clay minerals is the most effective criterion for the classification, because the concentration of pelagic clay minerals in which the Fe/Mg ratio is constant may become indices for the classification into the three types. The correlation coefficient and goodness-of-fit to a certain regression line were used as indices of the classification and calculated for several sets of modern sediments and ancient cherts totalling to more than 400 samples. The correlation coefficients and the student-t values for the coefficients become better classification indices than the goodness-of-fit andF-values of the analysis of variance. Goodness-of-fit andF-values can be only used as subsidiary indices for the main classification indices of the correlation coefficients. The classification on the basis of the degree of correlation between Fe and Mg is effective and this approach can be used for other major chemical elements such as Al, K, and Na, if some sequential values of chemical analyses are available.     

Sedimentary petrology and geochemistry of siliciclastic rocks from the upper Jurassic Tordillo Formation (Neuquén Basin, western Argentina): Implications for provenance and tectonic setting

The Upper Jurassic Tordillo Formation is exposed along the western edge of the Neuquén Basin (west central Argentina) and consists of fluvial strata deposited under arid/semiarid conditions. The pebble composition of conglomerates, mineralogical composition of sandstones and pelitic rocks, and major- and trace-element geochemistry of sandstones, mudstones, and primary pyroclastic deposits are evaluated to determine the provenance and tectonic setting of the sedimentary basin. Conglomerates and sandstones derived almost exclusively from volcanic sources. The stratigraphic sections to the south show a clast population of conglomerates dominated by silicic volcanic fragments and a predominance of feldspathic litharenites. This framework composition records erosion of Triassic–Jurassic synrift volcaniclastic rocks and basement rocks from the Huincul arch, which was exhumed as a result of Late Jurassic inversion. In the northwestern part of the study area, conglomerates show a large proportion of mafic and acidic volcanic rock fragments, and sandstones are characterised by a high content of mafic volcanic rock fragments and plagioclase. These data suggest that the source of the sandstones and conglomerates was primarily the Andean magmatic arc, located west of the Neuquén Basin. The clay mineral assemblage is interpreted as the result of a complex set of factors, including source rock, climate, transport, and diagenesis. Postdepositional processes produced significant variations in the original compositions, especially the fine-grained deposits. The Tordillo sediments are characterised by moderate SiO₂ contents, variable abundances of K₂O and Na₂O, and a relatively high proportion of ferromagnesian elements. The degree of chemical weathering in the source area, expressed as the chemical index of alteration, is low to moderate. The major element geochemistry and Th/Sc, K/Rb, Co/Th, La/Sc, and Cr/Th values point to a significant input of detrital volcanic material of calcalkaline felsic and intermediate composition. However, major element geochemistry is not useful for interpreting the tectonic setting. Discrimination plots based on immobile trace elements, such as Ti, Zr, La, Sc, and Th, show that most data lie in the active continental margin field. Geochemical information is not sufficiently sensitive to differentiate the two different source areas recognized by petrographic and modal analyses of conglomerates and sandstones.     

Cainozoic Stratigraphy of the lake Eyre basin and part of the arid region lying to the South

The Cainozoic history of the Lake Eyre region opened with a period of deep weathering during which many of the older rocks were extensively kaolinized. Following erosion and later deposition of a thin sheet of Tertiary fluviatile deposits, a period of weathering resulted in the widespread formation of silcrete. Another period of erosion and deposition was followed by soil formation and minor silici‐fication.

An important period of erosion followed during which some of the main elements of the present landscape were outlined. Warping during this interval gave rise to shallow basins in which lacustrine sediments accumulated. At about the same time, a system of mound springs developed near the western margin of the Great Artesian Basin. Another major period of erosion followed, by which time the main topographic features of the present landscape had evolved. This last event probably took place near the close of the Tertiary. Throughout the Tertiary, drainage was external and ancestral Lake Eyre remained fresh.

The Quaternary was characterized by four periods of aeolian and, to a lesser extent, water erosion and deposition alternating with periods of landscape stability, when weathering and soil formation took place.

Throughout the Cainozoic there was an alternation of relatively humid and dry periods, but true aridity and internal drainage did not appear until the Quaternary. Sand ridges were not formed until the late Quaternary. Intervals of gentle warping occurred from time to time during the Tertiary, but the Quaternary has for the most part been a period of stability. These events have given rise to a sequence of distinctive rock and soil‐stratigraphic units whose characteristics are considered in some detail.     

Litho- and Biostratigraphy of the Middle Neopleistocene of the European Northeast of Russia

The materials on litho- and biostratigraphy (collared lemming, Dicrostonyx) of the Middle Neopleistocene of the northeast Russia were revised and litho- and biostratigraphic methods were mutually tested for determination of the age of geological bodies. The reasonable stratigraphic division and correlation of the Neopleistocene are especially topical because of the current preparation of a new common stratigraphic chart of Quaternary sediments. The petrographic composition of the coarse-clastic material and the orientation of clasts in moraines are regionally consistent lithostratigraphic criteria. In the Pechora (Dnieper) moraine, the elongated rock clasts are oriented in a sector of 20°–60° in contrast to an azimuth of 270°–360° of the Vychegda (Moscow) moraine, which, in addition to petrographic composition of rocks, indicates the contribution of terrigenous material from different glacial provenances during formation of moraines. Certain differences were revealed also in assemblages of heavy minerals. The Middle Neopleistocene rodent fauna was found between the Pechora and Vychegda moraines. The stratigraphic position of microtheriofauna is identified on the basis of evolution level of molars of collared lemmings. By proportion of simplicior and henseli morphotypes for M1 and M2, all fossils belong to three groups corresponding to three evolution stages of a tooth system: Late Pechora (Late Dnieper, MIS 8), Rodionovo (Shklov, MIS 7), and Early Vychegda (Early Moscow, MIS 6). They include D. simplicior morph 2 (Gavrilovka, Bol’shaya Sluda, Akis’, Laya-4 localities), D. simplicior morph 3 (Sercheiyu-1, Laya-3 localities), and D. ex gr. simplicior—gulielmi (Shapkina-4, Chuley, lower horizon of Kipievo localities) morphs. These evolution stages correspond to Late Pechora (Late Dnieper, MIS 8), Rodionovo (Shklov, MIS 7), and Early Vychegda (Early Moscow, MIS 6) intervals. Taking into account the paleoclimate data, the presence of the lemmings in the region during the Rodionovo time is rather plausible.