As–(Ag) sulphide veins in the Spanish Central System: further evidence for a hydrothermal event of Permian age

The Spanish Central System (SCS) has been subjected to repeated deformation and fluid flow events which have produced both sulphide-bearing and barren vein systems. Although several hydrothermal episodes took place between 300 and 100 Ma, fluid circulation during the Permian was especially important, giving rise to a range of different types of deposits. This study presents a multidisciplinary approach leading to the characterisation of the chemistry and age of the hydrothermal fluids that produced the As–(Ag) mineralised stockwork of Mónica mine (Bustaviejo, Madrid). Fluid inclusion data indicate the presence of two different fluids. An initial ore stage (I) formed from a low- to moderate salinity (3–8 wt.% eq. NaCl) H₂O–NaCl–CO₂–CH₄ fluid, at minimum trapping temperature of 350±15 °C and 0.3 kbar. A second H₂O–NaCl fluid is found in three types of fluid inclusions: a high temperature and low salinity type (340±20 °C; 0.8–3.1 wt.% eq. NaCl) also associated to ore stage I, a moderate temperature and very low salinity type (160–255 °C; 0–1.5 wt.% eq. NaCl) represented in ore stage III, and a very low temperature and hypersaline type (60–70 °C; 30–35 wt.% NaCl), unrelated to the mineralising stages and clearly postdating the previous types. ⁴⁰Ar–³⁹Ar dating on muscovite from the early As–Fe stage (I) has provided an age of 286±4 Ma, synchronous with the late emplacement phases of La Cabrera plutonic massif (288±5 Ma) and with other Permian hydrothermal events like Sn–W skarns and W–(Sn) sulphide veins. δ¹⁸O of water in equilibrium with stage I quartz (5.3–7.7‰), δD of water in equilibrium with coexisting muscovite (−16.0‰ to −2.0‰), and sulphide δ³⁴S (1.5–3.6‰) values are compatible with waters that leached metamorphic rocks. The dominant mechanism of the As–(Ag) deposition was mixing and dilution processes between aqueous–carbonic and aqueous fluids for stage I (As–Fe), and nearly isobaric cooling processes for stages II (Zn–Cu–Sn) and III (Pb–Ag). The origin and hydrothermal evolution of As–(Ag) veins is comparable to other hydrothermal Permian events in the Spanish Central System.     

石英脉型钨矿原生晕特征及深部成矿定位预测——以赣南淘锡坑钨矿11号脉为例

以往对金、银、铜、铅、锌等矿床的原生晕研究较多,而对钨矿床原生晕的研究很少。为了探求新的钨矿找矿思路,更快速有效地圈定预测靶区、进而发现隐伏矿体,本文以原生晕轴向分带理论为指导,对赣南淘锡坑钨矿11号脉6个中段内沿脉所采的样品选取W、Zn、Au、Ag、Co、Mn、As、Sb及Ce、Hf、Lu和Yb来分析钨矿原生晕的结构,建立了该矿脉的原生晕叠加模型,继而预测靶区。结果表明,Zn、Au、Ag、Co、Mn、Ce、Hf、Lu和Yb异常晕与矿体中心的距离在50m范围内,为近矿晕指示元素;As、Sb异常晕发育于钨矿体前缘,与矿体中心相距200～250m,为前缘晕指示元素;根据该矿脉原生晕模型特征,预测了56m标高的3个靶位和-144m标高的3个靶位,其中靶位1和靶位2最具找矿潜力。     

构造叠加晕找盲矿法及其在矿山深部找矿效果

构造叠加晕找盲矿法是在发展了原生晕找盲矿理论基础上,根据热液矿床成矿成晕严格受构造控制,热液矿床具有多期多阶段叠加成矿成晕特点,提出原生晕叠加理论,解决了困惑化探专家几十年在研究原生晕轴向分带中出现的"反常"现象难题,独创了构造叠加晕找盲矿新方法,并介绍了构造叠加晕方法特点、主要成果、金矿床4种叠加结构的理想模式和盲矿预测的5条准则,应用效果和找矿实例。     

Geology and characterisation of the Pecket coal deposit, Magellan Region, Chile

The geology, petrography and chemical variation of the Pecket coal sequence, Magellan Region (52°57′S, 71°10′W), the only Chilean coal used for electricity generation on a large scale, has been studied in order to predict their combustion behaviour, especially in coal blends. The depositional environment of formation of the coal seams was a swamp rarely exposed to subaerial conditions and was associated with the development of the folded foreland of the Magellan basin during the Tertiary (Oligo–Miocene). The general tectonic regime of the collision of the Antarctic and South American plates is reflected by a system of joints with 40°N–50°W strike. The maceral composition of all six seams studied indicates high contents of vitrinite (>90%), minor content of liptinite (4.7%) and inertinite (<2%). Occurrence of tonstein horizons altered to kaolinite indicates a distal volcanism during peat accumulation. Coal rank varies between lignite and subbituminous (Ro=0.28–0.42%) with an average dry basis calorific value of 5450 kcal/kg, 17 wt.% moisture, 41 wt.% volatile matter, and sulphur content below 0.5 wt.%. The mineral matter (LTA) associated with the coal shows a dominance of kaolinite with quartz, smectite, and minor basanite. SiO₂/Al₂O₃ and Fe₂O₃/CaO ratios of the ashes diminish towards the lower seams. With respect to the utilisation of Pecket coals in combustion, base/acid ratios (B/A) and silica ratios (SR) indicate potential fouling for seams 1, 2, 5, and 6i, with high fouling indexes (Rf) for seams 2 and 5. Pecket coal is excellent for blend combustion due to its low sulphur content.     

山东蓬莱石家金矿原生晕地球化学特征及深部找矿预测

为预测和评价山东蓬莱石家金矿床的深部找矿远景,延长矿山服务年限,着重论述了该矿床的原生晕地球化学特征,对矿床的深部找矿潜力进行了探讨。原生晕元素组合特征分析表明,石家金矿床的矿体及近矿晕元素组合为Au、Ag、Cu、Pb、Zn、S、Te,前缘晕为Hg、As、Sb、Ba,尾晕为Mo、W、Sn。元素异常形态特征显示,326号矿脉南段以前缘晕和近矿晕为主,北段以前缘晕和尾晕为主,近矿晕元素异常较弱,矿体总体具有向南侧伏的特点。原生晕轴向分带序列在36线和84线均呈现反分带和前缘晕、尾晕共存的特点,结合地球化学参数在垂向上呈振荡波动变化的特征,说明矿体由多期次成矿作用叠加形成,同时预示矿体向深部还有一定延伸或有盲矿体存在。综合分析认为,326号矿脉南段为成矿的有利部位,深部仍有较大的找矿空间;矿体北段深部矿化减弱,但出现了前缘晕、尾晕元素的共存,预示深部可能还有盲矿体存在。     

Dispersion halos of elements around uranium ore bodies

Blind structurally controlled hydrothermal uranium ore bodies have definite geochemical expressions in their primary dispersion complex halos of lead, molybdenum, and soluble uranium extending over long distances upwards from the ores. Zonations in distribution-abundance of the three metals within the halos, as shown by orderly variations and trends in the ratios between the metals' concentrations, may serve by themselves as guides to the prospecting targets, under certain conditions — V.P. Sokoloff     

Autunian age constrained by fold tests for paleomagnetic data from the Mezarif and Abadla basins (Algeria)

A paleomagnetic study has been conducted on a formation dated as Autunian in the Nekheila area (31.4°N, 1.5°W) in the Mezarif basin. ChRM was thermally isolated in 117 samples from seven sites. This ChRM (D = 131.8°, I = 15.7°, k = 196, α₉₅ = 3.8° after dip correction; corresponding pole 29.3°S, 56.4°E) is very similar to that obtained in the neighboring Abadla basin from a formation of the same age. Fold tests associated with progressive unfolding applied to the full merged data from the dated formations of these two basins clearly indicate that the magnetization acquisition predates the deformation, which is attributed to the last phase of the late-Hercynian. The magnetization in these basins is therefore primary or acquired just after deposition. For the African Apparent Polar Wander Path, the age of the paleomagnetic poles of the Autunian part is now confirmed by paleomagnetic test.     

Seminar on geodynamics of the Himalayan region: Harsh. K. Gupta (Editor). National Geophysical Research Institute, India, 1973, 221 p., US $ 8.00

For a detailed palaeomagnetic research on Upper Permian red beds in the Wardha Valley (Central India) 265 samples from 47 sites at 6 localities were investigated.The samples from 3 localities (17 sites) appeared to be completely remagnetized during Early Tertiary times by the vast Deccan Trap flood basalts effusions. The samples from 22 sites of the other three localities (results from 8 sites rejected) could become cleaned from hard secondary Deccan Trap components by detailed thermal demagnetization.The resulting primary magnetization component reveals a mean direction (regardless of polarity, 7 sites normal, 15 sites reversed): D = 101.5°, I = +58.5°, α₉₅ = 6.5°, N = 3. This mean direction corresponds to a pole position at 129° W 4° N (dp = 7°, dm = 9.5°). This pole position fits well with other acceptable Late Permian—Early Triassic pole positions for the Indian subcontinent. From these acceptable results, a mean Permo-Triassic pole for the Indian subcontinent was computed at: 125° W 6°N. This Indian Permo-Triassic pole position, when compared with data from other Gondwanaland continents, suggests the hypothesis of an early movement between India and Africa before Permo-Triassic times.The partial or total remagnetization of some Indian red beds, mainly of Gondwana age, during Deccan Trap times is explained as acquisition of viscous Partial Thermoremanent Magnetization. This mechanism was advanced by Briden (1965), Chamalaun (1964) and Irving and Opdyke (1965).     

Electron paramagnetic resonance (EPR) spectroscopy in massive sulphide exploration, Rosebery mine area, western Tasmania, Australia

Electron paramagnetic resonance (EPR) spectroscopy of hot HNO₃ insoluble residues of rock powders is used as a new exploration technique for the volcanic-hosted massive sulphide (VHMS) deposit in the Rosebery mine area. The EPR signal intensities measured in 326.5±5 mT sweeps are strong in the altered rocks, and show a negative correlation with Ca, Na and Sr, and a positive correlation with K/Na, Rb/Sr and (K × Rb)/(Ca × Na × Sr). The EPR intensities measured in 326.5±100 mT sweeps show high values in the footwall pyroclastics, host rocks and hanging wall pyroclastics near and around the Rosebery deposit, and correlate positively with K, Fe, Mn, Ba, F, Rb, Zn, Pb and Zr. The Rosebery deposit and associated footwall alteration zone are located at the intersection of two elongated paramagnetic halos. The first is characterized by strong intensities of [AlO₄]° signals measured at magnetic flux density sweeps over 326.5±5 mT, trends NE–SW, and passes discordantly from the west to the east the White Spur Formation, altered footwall (footwall alteration zone), host rock of the Rosebery deposit, hanging wall and Mount Black Volcanics. The second, largely stratabound, halo is defined by strong intensities of Mn²⁺ sextets observed at magnetic flux density sweeps over 326.5±100 mT, runs N–S following the stratigraphic trend, and outlines the mineralized host rock and footwall alteration zone. It also extends toward the south into the unaltered footwall and hanging wall rocks. The first type of halo is considered to be related to wall rock alteration due to the VHMS mineralization processes as well to later Devonian metamorphism, and the second is thought to be related to massive sulphide mineralization alone.     

都龙矿区曼家寨矿段原生晕分带特征及深部找矿潜力评价

都龙矿区为滇东南多金属成矿系统(个旧—薄竹山—老君山)的重要组成部分。为评价曼家寨矿段深部找矿潜力,对其进行了原生晕分带的系统研究。研究表明:原生晕形态特征显示,前缘晕为Cd、As,近矿晕为Pb、Ag,尾晕为W、Mo;由格里戈良法获得轴向分带序列由浅至深为BiAs-Cu-Cd-Ag-Sb-W-Mo-Pb-Zn-Hg;根据原生晕轴向分带以及w(As)/w(Mo)、w(Cd×As)/w(W×Mo)等勘查评价指标由降转升的变化趋势,建立了原生晕叠加找矿模型。结合曼家寨矿段因子得分异常、主量元素找矿标志w(Fe+Na)等值线分布趋势,综合认为深部仍有良好的找矿前景。上述认识已得到探矿工程验证。     

Modeling outflow from the Ernest Henry Fe oxide Cu–Au deposit: implications for ore genesis and exploration

The Ernest Henry Fe oxide Cu–Au (IOCG) deposit (>ca. 1.51 Ga) is hosted by breccia produced during the waning stages of an evolving hydrothermal system that formed a number of tens of metres to a kilometre scale, pre- and syn-ore alteration halos, although no demonstrable patterns have been attributed to fluids expelled through the outflow zones. However, the recognition of a population of hypersaline fluid inclusions representing the ‘spent’ fluids after Cu–Au deposition at Ernest Henry provides the basis to model the geochemical characteristics of the deposit's outflow zones. Geochemical modeling at 300 °C was undertaken at both high and low fluid/rock ratios via FLUSH models involving three host rock types: (1) granite, (2) calc–silicate rock, and (3) graphitic schist. In models run at high fluid/rock ratios, all rock types are essentially fluid-buffered, and produce an albite–quartz–hematite–barite-rich assemblage, although in low fluid–rock environments, the pH, redox, and geochemical character of the host rock exerts a greater influence on the mineralogy of the alteration assemblages (e.g., andradite, Fe–chlorite, and magnetite). Significant sulphide mineralization was predicted in graphitic schist where sphalerite occurred in both low- and high-porosity models, which indicates the possibility of an association between high-temperature IOCG mineralization and lower temperature base metal mineralization.Cooling experiments (from 300 to 100 °C) using the ‘spent fluids’ predict early high-T (300–200 °C) Na-, Ca-, Fe-, and Mn-rich, magnetite-bearing hydrothermal associations, whereas with cooling to below 200 °C, and with progressive fluid–rock interaction, the system produces rhodochrosite-bearing, hematite–quartz–muscovite–barite-rich assemblages. These results show that the radical geochemical and mineralogical changes associated with cooling and progressive fluid influx are likely to be accompanied by major transformations in the geophysical expression (e.g., spectral and magnetic character) of the alteration in the outflow zone, and highlight the potential link between magnetite- and hematite-bearing IOCG hydrothermal systems.     

Palaeomagnetism of Upper Bhander Sandstones from Central India and implications for a tentative Cambrian Gondwanaland reconstruction

A virtual geomagnetic pole position for the uppermost Vindhyan sediments in Central India, probably correlative with the Cambrian of the Salt Range (W. Pakistan), was obtained from 43 oriented cores (7 sites) drilled from the Upper Bhander sandstones in the Great Vindhyan basin.Alternating field and thermal demagnetization resulted in a mean direction: D = 207.5°, I = +9.5° (k = 137.5, α₉₅ = 5.5°) and a virtual geomagnetic northpole position: 146.5° W48.5°N (dp = 3°, dm = 5.5°).This pole position disagrees with the Cambrian palaeomagnetic results from the Salt Range. Implications of this disagreement for the pre-drift configuration of Gondwanaland, based on palaeomagnetc results, are discussed.     

Halogen elements as indicator of deep-seated orebodies in the Chadong As–Ag–Au deposit, western Guangdong, China

Halogen elements play an important role in the metallogenesis of metallic ore deposits and are involved in the whole process of remobilization, transport and precipitation of metallic elements. However, with the exception of fluorine, which, as a component of fluorite and mica minerals, can be occasionally concentrated in ores, Cl, Br and I are hard to enrich in the ores. Investigations have found that the halogen elements tend to diffuse toward country rocks with the development of hydrothermal alteration in the process of their involvement in metallogenesis, especially during the post-ore stage when extensive halogen diffusion halos over orebodies would be formed. Such halogen element diffusion halos over the Chadong As–Ag–Au deposit extend as widely as 200 m. The largest diffusion extent is for I and the diffusion halos of Br are most noticeable 50–130 m away from the orebodies. In areas of ore exposure and the strongly altered zone, the Cl, Br and I contents are close to those of the strata with a V-shaped distribution pattern in the periphery of the mining district. Comparatively speaking, in going away from the altered zone, the major metallic elements Au and Ag in the deposit tend to decrease suddenly to their normal contents in the strata. This variation feature of halogen elements can be used as geochemical indicators for exploring concealed orebodies at depth. In the Chadong ore deposit, halogen element anomalies can be used to predict concealed orebodies at the depth range of 0–200 m.     

The geochemistry of arsenic and its use as an indicator element in geochemical prospecting

The geochemistry of arsenic is reviewed, and the use of the element as an indicator in geochemical prospecting for various types of mineral deposits is outlined.Arsenic is a widespread constituent of many types of mineral deposits, particularly those containing sulphides and sulpho-salts. In these and other deposits arsenic commonly accompanies Cu, Ag, Au, Zn, Cd, Hg, U, Sn, Pb, P, Sb, Bi, S, Se, Te, Mo, W, Fe, Ni, Co, and Pt metals. Under most conditions arsenic is a suitable indicator of deposits of these elements, being particularly useful in geochemical surveys utilizing primary halos in rocks, and secondary halos and trains in soils and glacial materials, stream and lake sediments, natural waters, and vegetation. Some of the natural arsenic compounds (e.g., arsine, dimethylarsine) are volatile, but methods utilizing gaseous arsenic halos for geochemical prospecting have not yet been developed.     

华南某地浸染型锯、钽花岗岩原生晕找矿的探讨

勘查地球化学作为一种找矿手段在寻找硫化多金属矿床方面日臻完善,应用愈益广泛并取得了令人满意的效果。然而对于浸染型铌、钽花岗岩矿床的地球化学找矿论述较少。事实上,此类矿床Nb、Ta矿物的颗粒细小,肉眼无法看到,除直观的地球化学找矿标志外,岩石地球化学找矿法和重砂法(即矿物晕法)是寻找和评价这类矿床的重要手段。     

Application of I / I to define the source of hydrocarbons of the Pol-Chuc, Abkatún and Taratunich–Batab oil reservoirs, Bay of Campeche, southern Mexico

Homogeneous ¹²⁹I / ¹²⁷I ratios from 6.51 ± 1.36 × 10^− 14 to 12.6 ± 1.49 × 10^− 14 were measured in formation brine at the Pol-Chuc, Abkatún, Taratunich–Batab off-shore oil reservoirs, Bay of Campeche in S-Mexico. Cosmogenic production could account for a homogeneous, Late Cretaceous/Paleocene time period (71.3 ± 5.3 to 56.3 ± 2.9 Ma) for the sedimentation and burial of organic material in the source formation. As the actual reservoir column is formed by Paleocene to Kimmeridgian sediments, the lower part of the lithological column must have received hydrocarbons that migrated downward from an initial source rock (Upper Cretaceous?) during a post-Paleocene event, probably during Miocene. Cosmogenic production from Tithonian shales can be excluded, as ¹²⁹I would have been decayed. As an alternative or complementary process, the subsurface, radiogenic production of ¹²⁹I / ¹²⁷I by ²³⁸U-fission in Uranium-enriched sediments should also be considered to explain the present, low ¹²⁹I / ¹²⁷I ratios.     

The geochemistry of antimony and its use as an indicator element in geochemical prospecting

The geochemistry of antimony is reviewed, and the use of the element as an indicator in geochemical prospecting for various types of mineral deposits is outlined.Antimony is widely diffused in many types of mineral deposits, particularly those containing sulphides and sulphosalts. In these and other deposits, antimony commonly accompanies Cu, Ag, Au, Zn, Cd, Hg, Ba, U, Sn, Pb, P, As, Bi, S, Se, Te, Nb, Ta, Mo, W, Fe, Ni, Co, and Pt metals. Under most conditions antimony is a suitable indicator of deposits of these elements, being particularly useful in geochemical surveys utilizing primary halos in rocks, and secondary halos and trains in soils and glacial materials, stream and lake sediments, natural waters, and to a limited degree vegetation. Some of the natural antimony compounds (e.g. stibine, dimethylstibine) are volatile, but methods utilizing gaseous antimony halos for geochemical prospecting have not yet been developed.     

内蒙花敖包特Pb-Zn-Ag多金属矿床原生晕分带特征与深部矿体预测模型

花敖包特Pb-Zn-Ag多金属矿床构造上位于滨西太平洋成矿域内蒙古大兴安岭成矿带南段, 是一个近年来发现的与白垩纪早期构造岩浆活动有关的隐伏热液脉状矿床.研究表明: (1)矿体原生晕发育, 且分带明显.据其异常强度建立的元素横向分带顺序(从强到弱)为Cd→Pb→Zn→Ag→Sb→In→Hg→As→Cu→Sn→W→Mo→Bi, 排在序列前面的Cd、Pb、Zn、Sb、Ag等5种元素, 可作为远矿指示元素; 排在序列后端的As、Bi、Mo、W等4种元素, 可作为近矿指示元素.(2)根据Grigorian原生晕分带计算方法, 获得矿体原生晕轴向分带序列(自矿体头部至尾部)为Sb→Pb→Cd→Ag→Zn→Hg→Cu→In→As→Bi→Sn→Mo→W, 与Grigorian建立热液矿床标准分带基本一致.(3)构建深部矿体找矿模型, 其预测评价指标(Sb×Pb×Cd×Ag)_D/(As×Sn×Mo×W)_D在矿体头部为1.30、矿体中上部为0.35、矿体中下部为0.056、矿体尾部为0.005, 这表明该指标随深度的增加有规律地降低, 是预测深部矿体资源潜力的有效指标.      

地球化学方法在吉家洼金矿区外围找矿中的应用

吉家洼金矿是华北陆块南缘熊耳山金矿田的一个小型矿床, 金矿体赋存于含矿断裂带内, 并严格受其控制, 矿体的形态、产状与含矿断裂基本一致。通过对矿区外围F1、F7断裂带开展系统的岩石地球化学测量, 圈定了多个受断裂控制的高强度Au异常, 经钻探施工, 见矿情况良好。进一步对钻孔进行了岩石原生晕采样化验和统计分析, 结果显示矿体向下有一定的延深, 经钻探施工, 在断裂深部发现工业矿体, 矿床规模扩大至中型。吉家洼矿区外围含矿断裂带数量多、矿化强度高, 而地表Au前缘元素非常发育, 向深部矿体头部元素及矿体元素发育并伴有前缘指示元素, 矿尾元素不发育, 已发现的矿体深部不封闭, 说明矿体沿倾向具有长距离延深, 深部找矿前景好。      

内蒙古锡林郭勒金成矿带物化探综合找矿方法研究

锡林郭勒金成矿带颇具找矿潜力,文章总结了成矿带的地球物理、地球化学特征,采用数理统计分析方法,确定了矿床元素轴向分带序列为:As-Sb-Hg-Bi-Li-Sr-Ba-Ag-Pb-Au-Cu-Zn-Sn-V-Co-Cr-Ni-Ti-Mo-W,前缘晕元素为As,Sb,Hg,Bi,主成矿元素为Au,Cu,Zn,尾晕元素为Ti,Mo,W.据轴向分带特征,确定金矿体剥蚀程度的判别指标为As×Sb×Bi/Ti×Mo×W.根据研究成果部署的深部钻探工程取得了较好的找矿效果.