Geochemical zoning of pyrite and arsenopyrite individuals from the Klyuchevskoe gold deposit,eastern Transbaikalia

Pyrite and arsenopyrite individuals were investigated in ore samples from the mesothermal Klyuchevskoe deposit. The internal structure of the individuals was determined by structural etching. Zoning of two orders was described. A correlation was established between the size of growth layers and the thickness of first-order zones. The anisotropic distribution of minor elements in particular zones and growth sectors was detected. It was found that the internal structure of metacrysts changes regularly, depending on their position relative to productive and nonproductive veinlets of different age. It was shown that, taking into account the volume effects of crystal growth, local changes in the geochemical parameters of mineral-forming medium (variations in trace element concentrations, density of mineral-forming solutions, character of temperature variations, etc.) can be estimated from variations in oscillation periods. The prospects of using pyrite-arsenopyrite and other geothermometers to study crystals consisting of several simple forms are discussed. It was concluded that the characteristics of the internal structure of pyrite metacrysts provide information on the stages of deposit formation.     

Subduction-related hot spring-type gold mineralization in the central Tengchong block,southwestern China

Numerous present-day hot springs and associated ancient Lianghe gold deposit occur in the central Tengchong block, SW China, associated with oceanic crust subduction. From the center outwards, the alteration zones in the hot spring of the Rehai consist of alunite and silica in a breccia zone, a kaolinite and illite zone, and a chlorite, illite, kaolinite zone. The gas phase in the hot spring is dominated by CO₂ with δ¹³C ranging from −4.5‰ to −7.2‰. These features indicate a major magmatic origin of the hot spring gas. The ³He/⁴He ratios in the gas from central Tengchong vary from 1.56 to 5.88, approaching to those of the MORB. This is probably related to the ongoing subduction of the Indian plate beneath the Tengchong block. The hot spring waters in the central Tengchong block have much higher content of Au and other elements, e.g., Ag, As, Sb, and Tl, than other typical hot springs, such as Hasbrouck, Sulfer, etc. in the world. The hot springs with more mantle gas contribution and higher water temperature show more elevated Au contents, which implies that the metal in the hot spring was most likely contributed from the magmatic gas. The compiled D-O isotopes of the hot spring waters from previous studies suggest that they are primarily derived from meteoric water. A genetic model for the hot spring system in the central of Tengchong has been tentatively established. The gold-charged hot spring is genetically connected to an active magma chamber, which was produced by subduction of oceanic crust. The chamber is driving long-term surface meteoric circulation and constantly releasing magmatic volatiles enriched with metals. As hot spring water mixed with magmatic volatiles, causing decompression-boiling and forming hydraulic fractures to penetrate the roof of siliceous sinter, which induced the continuing metal deposition and formed the Lianghe hot spring.     

Biogeochemistry of calcium and strontium in the landscapes of eastern Transbaikalia

This paper reports data on the contents and ratios of Ca and Sr in the soils, waters, and plants of eastern Transbaikalia and the Baikal region. The contents of Ca in the soils, waters, and plants of endemic areas affected by Urov disease approach those in objects from control areas. The contents of Sr in the soil–plant complex of the Urov biogeochemical province are relatively high and show spotted distribution, which is related to the landscape-geochemical characteristics of the region. It was found that the Ca/Sr values in the soils of a number of areas unaffected by Urov disease of animals and humans fall mainly within 11–236 (53 ± 24 on average). In the soils of endemic regions in eastern Transbaikalia, Ca/Sr ranges from 2 to 98 (36 ± 11 on average). The hay crop of meadow plants show Sr contents of 72.8 ± 31.6 mg/kg (endemic region) and 36.6 ± 15.7 mg/kg (control areas) and Ca/Sr values of 250 ± 115 and 525 ± 382, respectively. The elevated Sr content in the soils and plants of the endemic region is considered as a factor of ecological risk.     

Geochemical specifics of ongonites in the Ary-Bulak Massif, eastern Transbaikalia

A genetic model for magmatic rocks of the Ary-Bulak Massif is discussed based on a detailed geological map of the massif (prepared by the authors) and on original data of the authors on the petrography of the massif, its compositional zoning, trace-element geochemistry, physicochemical parameters of its crystallization, and melt inclusions in its minerals. The Ary-Bulak Massif was determined to be zonal, with the predominance (approximately 70% by area) of porphyritic topaz ongonites (central facies), which grade toward contacts into weakly porphyritic ongonites bearing topaz and, occasionally, fluorite (margin facies). Aphyric rocks with fluorite (inner-contact facies) occur as a stripe 50–80 m wide at the southwestern inner contact of the massif. Analysis of petrographic and geochemical data indicates that subvolcanic rocks of the Ary-Bulak Massif differ from typical elvanes (as they occur in the Cornwall province) but are similar to classic ongonites in the central and marginal facies of the massif. Rocks in the southwestern inner-contact zone are unusual high-F and high-Ca varieties, whose analogues have never been found in any rare-metal provinces with ongonites and which provide evidence of a complicated evolutionary history of the Ary-Bulak Massif. The geochemical evolution of this massif was determined to be characterized by the enrichment of the older inner-contact facies rocks in CaO, K₂O, F, and Rb, Cs, B, Ba, Sr, Sn, and Ta, whose concentrations decrease in the ongonites of the central facies. The central-facies ongonites thereby have much higher Na₂O and Li concentrations than those in the inner-contact facies rocks. It is demonstrated that the intense heating and melting of crustal material in this region at the Jurassic-Cretaceous boundary could have been induced by subalkaline basaltic magma. The chemical composition of the rocks, which is unusual for typical ongonites in, for example, high Ca and Sr concentrations, could be caused by the possible assimilation by the magma of limestones, which occur in the territory at a certain depth in the Ust’-Borzya Formation that hosts the Ary-Bulak Massif. The genesis of most rocks in the massif was controlled by the magmatic differentiation of crustal granitic magma, with the residual melts forming Li-F granites enriched in several trace elements (Li, Rb, Cs, B, Ba, Sr, etc.) and ongonites as their subvolcanic analogues.     

黔西南中部卡林型金矿床冲断褶皱构造的地震 勘探证据及意义

地震勘探资料对黔西南中部卡林型金矿赋存层位上二叠统龙潭组煤系地层、东吴不整合面和广西不整合面显示良好。该地区卡林型金矿主要受冲断褶皱构造的控制。在地震剖面上,根据卡林型金矿在冲断褶皱构造中的位置,可以将其划分为两类,即断层控制型金矿和断层伴生型金矿。在断层控制型金矿床中,断层 “上陡下缓”,为低角度逆冲断层,断层上盘常发育不对称背斜构造,断层向下在上二叠统龙潭组煤系地层、“大厂层”凝灰岩和东吴运动形成的不整合面间滑脱,金矿体产于低角度逆冲断层中,在浅部为脉状矿体,在深部渐变为缓斜穿层矿体。断层伴生型金矿床发育于由高角度断层引起的层间滑动带,呈似层状。印支晚期华南古特提斯洋的相继闭合是形成北西向和北东向两组主要冲断褶皱构造的主控因素。地震勘探资料揭示,黔西南中部还存在与已经发现卡林型金矿的冲断褶皱构造带类似的构造,找矿前景较好。     

Late Paleozoic granitoid magmatism of Eastern Kazakhstan and Western Transbaikalia: plume model test

We present results of a comparative study of Late Paleozoic granitoids of Eastern Kazakhstan and Western Transbaikalia composing the large Kalba-Narym and Angara-Vitim batholiths. We have established that despite the different geologic history of these regions, granitoid magmatism there proceeded nearly synchronously at the Carboniferous/Permian boundary (330–280 Ma) and was accompanied by mantle magmatism. The regularities of its evolution are considered in terms of the plume model and different stages of interaction of mantle plumes with the lithosphere. The major principles of plume-lithosphere interaction in accretion-collision fold belts have been formulated: (1) Plume-lithosphere interaction results in large-scale melting of sublithospheric mantle, lower lithosphere, and crustal substrates warmed by the preceding orogenic processes; (2) The processes last 30 to 50 Myr and produce large volumes of igneous rocks, mostly granitoids; (3) The sequence of formation of granitoid and basic igneous complexes and the metallogenic specialization can be different and depend on the lithosphere structure and preceding geologic history of the region.     

Metasomatites of the Kara gold deposit (Eastern Transbaikalia)

Wall-rock metasomatites of the Kara gold deposit, a high-temperature medium-depth pneumatolytic-hydrothermal formation, have been studied. Gold mineralization is associated with the intrusion of granitoids of the Kara-Chacha massif (J3) and dikes of alkaline rocks (J3-K1), which include hybrid porphyries, “grorudites”, etc. They are characterized by telescoping of ores, expressed best of all on joints of ore-bearing sites.The origin of the Kara-Chacha massif (Amudzhikan-Sretensk complex) is connected with pre-ore areal propylitization. The propylites demonstrate a zonal pattern relative to the massif and ore veins. A composite metasomatic column of propylitized rocks has been compiled.The thickness of intensely altered wall rocks does not exceed 1.5–2.0 m and the structure of these zones is very heterogeneous. Syn-ore metasomatites are found in propylitized rocks. The major factor of syn-ore alteration of host rocks is the active behavior of alkaline elements. Albitization, silicification (in separate sites), tourmaline and pyrite alteration occur at the early quartz-pyrite-tourmaline stage of mineralization. Sodium is supplied at this stage. During the next quartz-actinolite-magnetite stage sodium and potassium are active. The host rocks demonstrate albitization, feldspar alteration, silicification, actinolitization, biotite alteration, and magnetite impregnation. Aegirine in veins is accompanied by occurrence of aegirine, alkaline amphibole, green biotite and, locally, quartz in host rocks. Potassium becomes more significant later, reaching the maximum activity at the quartz-sulfide stage. The development of quartz-arsenopyrite assemblage was accompanied by K-feldspatization, sericitization of host rocks, formation of green and tan biotites, and arsenopyrite impregnation. The formation of K-feldspar, sericitization, silicification, and sulfide impregnation are associated with quartz-sulfide ore. The final quartz-carbonate-polymetallic stage is accompanied by silicification and carbonate alteration of host rocks. Potassium becomes increasingly more active from outer zones of metasomatic columns to inner ones. The gold contents tend to increase with the potassium contribution in zones of hydrothermal alterations.The propylite alteration and syn-ore changes become more intense veinward. It can indicate that hydrothermal solutions with dissolved minerals penetrated through the most reworked zones. However, hydrothermal solutions during propylite alteration and later syn-ore changes of host rocks not always penetrated through the same zones of weakness, such as tectonic dislocations, contacts of various rocks, etc. The rocks, comprising inner zones of the metasomatic column of propylites are quite often observed at a certain distance from veins and accompanied inner zones of metasomatic columns of later syn-ore metasomatites. They sometimes are not associated with ore veins. However, they are demonstrate later superimposed threads and separate impregnations of syn-ore minerals.Abundant telescoping of mineralization and inheritance of mineralization stages complicate the structure of zones with syn-ore metasomatites. In the sites with telescoped mineralization the metasomatites contain minerals intrinsic to all stages of mineralization found at the deposit.     

Dike swarms and related igneous complexes in the Urals

The dike swarms of the entire Urals are classified for the first time; the related igneous complexes associated with them in space and time are named. The following types and chronological levels of the Uralian dikes are distinguished (proper names are given after type localities). The epicontinental type comprises the Middle Riphean Mashak, Late Riphean Arsha-Serebryanka, Late Cambrian-Early Ordovician Kidryasovo-Lemva, Ordovician-Silurian Ushat, Devoninan Inzer-Timaiz (the most extended of all), Early Carboniferous Magnitogorsk-Mugodzhary, and Triassic Borisovo dike swarms. Many of them are probably related to plume events. The existence of the Early Riphean dike complex remains unclear. Oceanic (spreading or suprasubduction) dike-in-dike type: Ordovician Man’ya oceanic type, Devonian Aktogai backarc and Khabarny suprasubduction types. The igneous complexes associated with dike swarms are rather diverse. In addition to rhyolite dikes, in many cases determining the contrasting character of magmatism, large comagmatic gabbro and gabbro-granite intrusions are noted, as well as minor intrusions of subalkali granitoids, syenites, and, apparently, carbonatites and kimberlites. Flood basalt fields are noted at the periphery of the Urals, implying the occurrence of a feeding dike swarm beneath them.     

Proglacial damlakes in eastern Transbaikalia: New insight into the Pleistocene paleogeography

Paleogeographic reconstructions for the Samarovo, Taz, Murukta, and Sartan glaciations reveal the formation conditions of proglacial lakes dammed by ice in intermontane depressions and valleys of large rivers in eastern Transbaikalia. Middle-Late Pleistocene climate change is reconstructed using spore-pollen spectra from Pleistocene sediments in northern Transbaikalia. The age and lifetime of proglacial lakes are constrained by radiocarbon, thermoluminescence, and varve chronology of their bottom sediments in the periglacial zone. The lake levels remain recorded in sediments produced by deposition and erosion along the former lake shores, as well as in morphology and lithology variations of terminal moraines. A large proglacial lake, with a maximum level of 1020 m, occupied vast areas in Transbaikalia and its surroundings during the Samarovo glaciation. After the glaciers degraded, the Amur River system expanded into the area of closed lake basins in the southeastern Baikal region, including North China and Mongolia. The obtained results have implications for the Middle-Late Pleistocene history of lake deposition.     

Application of mineral thermometers and barometers to granitoid igneous rocks: the Etive Complex, W Scotland

Summary The Etive complex, one of the Caledonian Newer Granites of Scotland, is a ring complex of Devonian age, ranging in composition from pyroxene-diorite to leucogranite. Six samples, representing the major rock units in the southern parts of the Etive complex were chosen for mineral chemical studies and for estimation of the pressure and temperature conditions of magmatic crystallisation. Application of Al- in-hornblende barometry and crossite contents of amphiboles indicates a pressure <3kbar for the intrusion, in good agreement with published independent pressure estimates of 2kbar from mineral equilibria in metasedimentary hornfelses in the Etive thermal aureole. Thermometry, using ternary and binary feldspar systems, yields low temperatures, which probably reflect late-stage, post-magmatic re-equilibration of these minerals. Several geothermometers have been applied to the Quarry Diorite, the outermost intrusion of the complex. The highest temperature for the rocks comes from orthopyroxene–clinopyroxene solvus thermometry, and is 1000°C; this is interpreted to reflect the initial crystallisation of the diorite magma immediately after its emplacement. The maximum temperature from hornblende-plagioclase thermometer is 816°C, which probably reflects late-stage crystallisation of the magma.     

Composition and formation conditions of sediments in the Doroninskoe soda lake (eastern Transbaikalia)

It has been established that the southern and eastern parts of the Doroninskoe soda lake bottom with the depth less than 4–4.5 m are mainly composed of micrograined quartz-feldspar sand. Silty-clayey kaolinite-hydromica particles predominate from the depth more than 4–4.5 m. Low maturity of clastic material and its insignificant role in the formation of soda minerals in the lake have been established. Very high concentrations of Cl and Na, as well as high concentrations of S and P, are specific characteristics of the chemical composition of sediments. Distribution of chemical elements is governed by a complex action of the mechanical, alkaline, sorption, and hydrosulfuric barriers. With increasing depth and distance from the shore, concentrations of Ti, Ce, Na, Mn, La, Ca, Co, and Cu increase by 3–3.5 times; Fe, P, V, and Zn, by 4.5–5 times; Mg, Ni, and Cr, by 6–7.5 times; and Cl and S, by 10–15 times. The sharp increase in the contents of Ti, Fe, Mn, Ce, and La is related to the formation of zircon-ilmenite placer horizons. Concentrations of Si, K, and Ba show negative correlation with the psammite component. The Pb content does not depend on the barrier factor.     

Jurassic sediments in the Irkut basin and southwestern Transbaikalia: correlations based on paleobotanical and geochronological data

The Jurassic growth of mountain ranges along the southern edge of the Siberian platform occurred in an active tectonic setting related to the closure of the Mongol-Okhotsk Ocean. The oceanic subduction and subsequent continent collision events induced compressive deformations at the platform boundary. Understanding the paleogeography related to the Mesozoic closure of the Mongol-Okhotsk Ocean requires dating and correlation of the Jurassic Prisayan Formation in the Irkut basin and Tugnuyskaya Formation in southwestern Transbaikalia. This work presents structural and paleobotanic results within both formations. ⁴⁰Ar/³⁹Ar dating of underlying volcanics from the upper member of the Ichetuyskaya Formation is used to refine the age of the sediment series and provide probable correlation. The results show that the Tugnuyskaya Formation initiated at the end of the Middle Jurassic-beginning of the Late Jurassic and was not coeval with the Prisayan Formation, whose upper fine-grained members were deposited in the early Middle Jurassic. ⁴⁰Ar/³⁹Ar dating of volcanics from the upper member of the Ichetuyskaya Formation yielded a Middle Jurassic age of 167.7 ± 1.2 Ma (Bajocian to Bathonian). The paleogeographic data analysis based on facies and mineralogical composition of sediments and on a study of source areas from Sm-Nd data and the U-Pb ages of detrital zircons from the deposits in the southern Irkut basin indicates that the deposition of the Prisayan Formation was followed by the intensification of relief building along the southern edge of the Siberian Platform. Our geochronological data show that active tectonic deformations in southwestern Transbaikalia evidenced in the volcanoclastic Ichetuyskaya Formation in the Tugnuy basin also occurred during the Middle Jurassic. The uppermost sediments of the Tugnuy basin were deposited at the end of the Middle Jurassic-Late Jurassic in a quiet tectonic setting with low relief and lacustrine-boggy depositional environments.     

湘东雁林寺金矿田及邻区构造变形事件与控矿构造属性

雁林寺金矿田位于湘东北金矿区南部,发育大量中小型金矿床（点）。前人对区内包括控矿构造在内的各类变形的运动学特征及形成时代和机制尚缺乏探讨和解析,从而影响到对矿床形成和保存规律的全面认识。鉴此,笔者等基于区域构造特征和大量露头构造的详细解析,厘定了雁林寺金矿田及邻区的构造变形序列及其时代背景,并结合矿床地质和同位素测年等其他资料,探讨了成矿时代和控矿构造属性。主要认识如下：① 研究区自早至晚经历了新元古代中期NW—SE向挤压、志留纪早期NW—SE向挤压、志留纪末花岗岩体主动侵位挤压、中三叠世晚期NW—SE向挤压、晚三叠世NNW—SSE向—S—N向挤压、中侏罗世晚期NWW—SEE向—近E—W向挤压、白垩纪NW—SE向伸展、古近纪中晚期NE—SW向—NNE—SSW向挤压、古近纪晚期—新近纪初NW—SE向挤压等9期构造事件,形成了不同走向和规模的褶皱、逆断裂、顺层剪切带、正断裂、右行和左行走滑断裂与剪切破裂、断陷盆地、劈理、膝折等构造类型,以及部分构造走向的后期偏转。② 区内存在志留纪末和晚三叠世两期金成矿作用,均与同期花岗质岩浆活动有关。③ 雁林寺金矿田容矿构造主要有前中生代顺层脆韧性剪切带和层间断裂、中—晚三叠世的NW向—NWW向右行走滑断裂和剪切裂隙、花岗岩枝的内外接触带等3类。志留纪末金矿床的导矿构造为先期NE向深部逆断裂,晚三叠世金矿床的导矿构造为中三叠世晚期的NE向逆断裂、晚三叠世早期的NEE向和EW向逆断裂。对两期金矿床而言,成矿后各期变形事件中形成的不同类型断裂均可能成为破矿构造。     

Fluid and magmatic processes in the formation of the Ary-Bulak ongonite massif (eastern Transbaikalia)

The paper discusses the formation conditions of the Ary-Bulak ongonite massif (eastern Transbaikalia). Studies of melt and fluid inclusions have shown that, along with crystalline phases and a silicate melt, ongonitic magma contained aqueous–saline fluids of different types, fluoride melts compositionally similar to fluorite, sellaite, cryolite, chiolite, and more complex aluminum fluorides as well as silicate melts with abnormal Cs and As contents. An ongonite melt crystallized with the participation of P–Q fluids as vapor solutions, presumably NaF-containing and slightly admixed with chlorides. We studied the properties and composition of brine inclusions from Ca- and F-rich rocks on the margin of the massif. Depending on the thermophysical properties of the host rocks and ongonite melt, the duration of its crystallization has been estimated for a magma chamber of the size and shape of the Ary-Bulak massif. Magma chamber cooling has been modeled, and the density, viscosity, and Rayleigh number of the ongonite melt have been estimated from the composition of silicate glasses in melt inclusions. These data strongly suggest intense convection in the residual magma chamber lasting for centuries. We have calculated possible fluid overpressure during the crystallization and degassing of the ongonite melt in a closed magma chamber.Calcium- and fluorine-rich aphyric and porphyritic rocks on the southwestern margin of the massif might have formed by the following mechanism. Local decompression in the magma chamber quenched an oxygen-containing calcium fluoride melt accumulated at the crystallization front, and then these rocks altered during the interaction with fluids. When penetrating the marginal zone, a P–Q magmatic fluid which coexisted with the melt in the residual chamber cooled and changed its composition and properties. This caused the fluid to boil and segregate into immiscible phases: a vapor solution and a brine extremely rich in Cl, F, K, Cs, Mn, Fe, and Al. The fluoride and silicate liquids were immiscible; the silicate melts had abnormal Cs and As contents; changes in the composition and properties of the magmatic fluids caused them to boil and produce brines. All this is evidence for complex fluid–magma interaction and heterogeneous ongonitic magma during the crystallization of the Ary-Bulak rocks. These processes were favored by the low viscosity and high mobility of the F- and water-rich ongonite melt, intense melt convection in the residual chamber, and rising fluid pressure during its degassing.     

湘东雁林寺金矿田及邻区构造变形事件与控矿构造属性

雁林寺金矿田位于湘东北金矿区南部,发育大量中小型金矿床（点）。前人对区内包括控矿构造在内的各类变形的运动学特征及形成时代和机制尚缺乏探讨和解析,从而影响到对矿床形成和保存规律的全面认识。鉴此,本文基于区域构造特征和大量露头构造的详细解析,厘定了雁林寺金矿田及邻区的构造变形序列及其时代背景,并结合矿床地质和同位素测年等其他资料,探讨了成矿时代和控矿构造属性。主要认识如下：（1）研究区自早至晚经历了新元古代中期NW—SE向挤压、志留纪早期NW—SE向挤压、志留纪末花岗岩体主动侵位挤压、中三叠世晚期NW—SE向挤压、晚三叠世NNW—SSE向—S—N向挤压、中侏罗世晚期NWW—SEE向—近E—W向挤压、白垩纪NW—SE向伸展、古近纪中晚期NE—SW向—NNE—SSW向挤压、古近纪晚期—新近纪初NW—SE向挤压等9期构造事件,形成了不同走向和规模的褶皱、逆断裂、顺层剪切带、正断裂、右行和左行走滑断裂与剪切破裂、断陷盆地、劈理、膝折等构造类型,以及部分构造走向的后期偏转。（2）区内存在志留纪末和晚三叠世两期金成矿作用,均与同期花岗质岩浆活动有关。（3）雁林寺金矿田容矿构造主要有前中生代顺层脆韧性剪切带和层间断裂、中—晚三叠世的NW向—NWW向右行走滑断裂和剪切裂隙、花岗岩枝的内外接触带等3类。志留纪末金矿床的导矿构造为先期NE向深部逆断裂,晚三叠世金矿床的导矿构造为中三叠世晚期的NE向逆断裂、晚三叠世早期的NEE向和EW向逆断裂。对两期金矿床而言,成矿后各期变形事件中形成的不同类型断裂均可能成为破矿构造。