Carbonate alteration of the Upper Mount McRae Shale beneath the martite-microplaty hematite ore deposit at Mount Whaleback, Western Australia     

Adam D. Webb  Gerald R. Dickens  Nicholas H. S. Oliver 《Mineralium Deposita》2004,39(5-6):632-645

The formation of large martite-microplaty hematite ore deposits in northwest Australia remains a contentious topic in part because important evidence supporting a unifying genetic model has not been observed at all deposits. Carbonate replacement of silica has been found along normal faults below ore at the Mount Tom Price and Giles Mini deposits, which suggests an early hypogene process during ore formation. However, such rocks have not been identified at the largest martite-microplaty hematite deposit, Mount Whaleback. In this study, samples of the Mount McRae Shale are examined for their chemistry, mineralogy and petrography. These samples were collected from several key locations, including an area that immediately underlies ore along the Mount Whaleback fault at Mount Whaleback. Compared to unaltered black Mount McRae Shale from Wittenoom Gorge in the north and altered black and red Mount McRae Shale at Mount Whaleback, reddish-green Mount McRae Shale along the Mount Whaleback fault is greatly enriched in MgO and CaO and depleted in SiO₂. This chemistry arises from significant amounts of fine- to medium-grained ferroan-dolomite and ankerite and cross-cutting chlorite and carbonate veins. The composition is distinct from that produced during regional metamorphism, and most likely represents hydrothermal alteration after metamorphism. The lack of carbonate-rich, silica-poor rocks in the overlying Dales Gorge Member at Mount Whaleback is consistent with pervasive oxidation of most rocks in the region during or after ore genesis, a process that removed carbonates. Although several questions remain unanswered, these results support models that invoke an early hypogene stage during the formation of the martite-microplaty hematite deposits in the Hamersley Province.Editorial Handling: B. Lehmann  相似文献   

Comparison of particle size characteristics of the Tertiary 'red clay' and Pleistocene loess in the Chinese Loess Plateau: implications for origin and sources of the 'red clay'   总被引：7，自引：0，他引：7  

S. L. Yang  Z. L. Ding 《Sedimentology》2004,51(1):77-93

The origin of the Tertiary ‘red clay’ underlying the Pleistocene loess in the Chinese Loess Plateau remains controversial, although several lines of evidence have suggested a wind‐blown origin. This study examines the particle‐size parameters of the late Miocene and Pliocene ‘red clay’ by comparing it with those of the late Pleistocene loess. The particle‐size distribution of a total of 15 339 loess and 6394 ‘red clay’ samples taken from 12 loess sections along a north–south transect and two ‘red clay’ sequences at Lingtai and Jingchuan was systematically analysed. The median grain size, skewness and kurtosis of the late Pleistocene loess all show a systematic southward change and are principally influenced by distance from source region. The spatial and temporal differentiation of dust deposits is expressed in a skewness–kurtosis–median grain size ternary diagram, from which the distance to the source region can be inferred. The particle‐size characteristics of the Tertiary ‘red clay’ sediments are very similar to those of the palaeosols within the late Pleistocene loess deposits, suggesting an aeolian origin for the ‘red clay’. Based on the comparison of ‘red clay’ and loess in the ternary diagrams, it is inferred that the source–sink distance was greater in the Neogene than in the last and penultimate interglacials, and that the dust source region in north‐western China underwent a progressive expansion during the period from at least 7·0 Ma to the present.  相似文献   

Alkali-rich igneous rocks and related Au and Cu large and superlarge deposits in China   总被引：6，自引：1，他引：6  

赵振华  熊小林  王强  包志伟  张玉泉  谢应雯  任双奎 《中国科学D辑(英文版)》2003,46(Z1)

The alkali-rich igneous rocks in China occur as fifteen linear distributed belts of each extending several hundreds to several thousands kilometers in length. These include most types of alkali-rich igneous rock categories discovered worldwide. The related Au, Cu large and superlarge deposits or metallogenic focus-areas include Dongping, Guilaizhuang, Yulong, etc. Direct and indirect genetic links have been found between alkali-rich igneous rocks and Au, Cu mineralization. The petrogenesis and metallogenesis of the alkali-rich igneous rocks are mainly controlled by (1) mantle enrichment, (2) strong interaction between mantle and crust, (3) lower contens of sulfur, high and high contents of volatiles, (4) the significant turn of regional tectonic framework from compress to extension and (5) the strong change of regional lithosphere structure.  相似文献   

Discovery of the copper deposits with features of the Keweenawan type in the border area of Yunnan and Guizhou provinces   总被引：1，自引：0，他引：1  

朱炳泉  胡耀国  张正伟  常向阳 《中国科学D辑(英文版)》2003,46(Z1)

There existed intense Cu anomaly on the northeastern side of the geochemical boundary with NW strike in the border area between the Yunnan and Guizhou provinces. Through field observation, ore bodies of high-grade native coppers have been found. The copper mineralization was constrained by the ancient volcanic vents of Permian basalt eruption and the overlain strata of carbonaceous argillites. Native coppers with flaky, net veined and impregnated occurrences, fine-grained tenorites and massive chalcocites widely occur in volcanic breccias, tuffs, carbonaceous-siliceous argillites and siliceous bitumen rocks with bed thickness of about 15-80 m. Cu contents vary from 0.5% to 20%. The copper mineralization was tightly related to actinolite-tremolitization, zeolitization and bituminization and involved in extensive reduction environments. Continental flood basalts erupted in mantle plume environments usually have high Cu concentrations (～170 ×10-6 in the Emeishan basalts), which provided a copper source of mineralization. Thus, metallogenesis of the native copper deposits in the Yunnan-Guizhou border area is tightly associated with intensive crust-mantle and organic-inorganic interactions. The tremolitization and chalcocitization indicate that the metallogenic temperatures are in a range of 400-100℃. The geologic background and characteristics of ore and alteration for the native copper deposits in this area are somewhat similar to those of the Keweenawan native copper deposit in Michigan, USA.  相似文献   

念青唐古拉山东南麓更新世冰川沉积物年龄测定   总被引：14，自引：6，他引：14  

吴中海  赵希涛  江万  吴珍汉  朱大岗 《冰川冻土》2003,25(3):272-274

在念青唐古拉山南北两麓及切割山脉的各沟谷中 ,分布着 3套更新世冰川与冰水沉积物 ,其冰水沉积物的电子自旋共振 (ESR)和光释光 (OSL)测年结果分别为 ( 5 93± 2 6 0 )kaBP与 ( 6 78± 30 7)kaBP ,( 2 0 5± 5 4 )kaBP和 ( 2 5 4± 8 7)kaBP .测年结果表明 ,在念青唐古拉山东南麓所发生的 3次冰川作用 ,分别相当于青藏高原南部的聂聂雄拉冰期、古乡冰期和白玉冰期  相似文献   

西藏纳木错第四纪湖泊沉积与湖成地貌--兼论藏北高原古大湖问题   总被引：3，自引：2，他引：3  

朱大岗  赵希涛  孟宪刚  吴中海  邵兆刚  吴珍汉  杨超斌  王建平 《吉林大学学报(地球科学版)》2003,33(2):156-162

对西藏面积最大的湖泊——纳木错湖相沉积野外现察结果，发现了由水平层理十分发育的砂与粘土所组成的、高出湖面分别为3—12m、15—22m、25—30m与35—45m的4级湖岸阶地，覆于基岩之上、高出湖面60—150m的湖相沉积和多达50条左右、由扁圆湖滨相砾石所组成的湖岸堤，环湖广泛分布的湖成地貌。在连结纳木错与其西北的仁错约玛、仁错贡玛、久如错的分水岭宽谷底部(分别高出上述3湖20m、90m与60m)与北侧山坡，即纳木错的第二与第三级湖岸阶地，发现了组成阶地与异堤的湖相与湖滨相沉积。从而确证了纳木错与仁错-久如锴曾多次连通，即数度成为一个统一的大湖，而不是以河道相连的不同湖泊。古大湖分离时代为末次冰期间冰段。  相似文献   

Epiclastic deposits and ‘horseshoe-shaped’ calderas in Tahiti (Society Islands) and Ua Huka (Marquesas Archipelago), French Polynesia     

Jean-Philippe Clment  Christelle Legendre  Martial Caroff  Herv Guillou  Joseph Cotten  Claire Bollinger  Grard Guille 《Journal of Volcanology and Geothermal Research》2003,120(1-2):87-101

Occurrences of debris avalanche deposits newly identified in Tahiti (Society Islands) and Ua Huka (Marquesas Archipelago) are described and interpreted here. In both islands, the breccias are located within horseshoe-shaped residual calderas. In Tahiti, the epiclastic formations, up to 500 m thick, lie on the floor of the central depression and in the valley of the northwards running Papenoo River. In Ua Huka, the breccias crop out within a depression limited by a semicircular crest in four bays along the southern coast. Their thickness is ca. 100 m. A few clasts collected in the Tahitian breccias and some rocks forming their substratum have been dated (K–Ar datings) and analysed (major and trace elements, Sr–Nd isotopes) for this study. Using these data, we show that the debris avalanche(s) occurred in Tahiti Nui at the end of the growth of the shield volcano (between 570 000 and 390 000 years ago), maybe in consequence of the emplacement of the plutonic body which occupies the central part of the caldera. In Ua Huka, the collapse took place nearly 3 Ma ago, between the construction of the shield volcano and that of the inner one. The southwards orientation of the caldera, like that of the neighbouring island Nuku Hiva, might reflect a preferential direction of weakness in the substratum of the central Marquesas.  相似文献   

新疆若羌县红十井金矿地质特征及深部成矿预测   总被引：2，自引：0，他引：2       下载免费PDF全文

周济元  崔炳芳等 《地质学报》2003,77(1):104-112

红十井金矿，产于中，上石炭统基性火山岩和火山碎屑岩中，为受断裂带控制的韧性剪切带型金矿床，原认为主矿体南倾，未查明侧伏方向，在体南侧和中，东段布钻，深部未打到矿体，仅求得0．947t金储量。笔者等经地质构造，矿体空间展布形式，矿物热电性和电磁场测深等研究，预测主体北倾，西挺，南西西侧伏，北东东仰起，在主矿体北侧和中、西段布钻，结果在深部和中、西段均打到了矿体，金储量由0．47t增加至10．1t以上，取得了突破性进展。  相似文献   

内蒙古白乃庙地区金矿成矿作用   总被引：5，自引：1，他引：5  

李进文  王存贤  侯万荣  修群业  臧文拴  李尚林 《现代地质》2003,17(3):275-280

内蒙古白乃庙金矿床为石英脉型和石英脉+蚀变岩型金矿,赋存于海西期的岩浆岩和白乃庙组的绿片岩中。海西期的石英闪长岩和斜长花岗岩的金丰度值为9 0×10-9～15 0×10-9,矿石铅同位素与海西期斜长花岗岩的铅同位素组成相似,反映成矿母岩可能为矿区的海西期岩浆岩;硫化物铅同位素的Δγ和Δβ值及硫同位素δ34S值显示成矿物质来源于深部,与岩浆岩有关;石英流体包裹体的δD水值、计算得出的δ18O水值和方解石的δ13C值表明成矿流体起源于岩浆,演化过程中有大气降水的加入。成矿作用是在区域构造体制发生转换后,于伸展地球动力学环境下进行的,成矿期控矿构造均呈张性,具有多阶段活动的特点。Au在成矿热液体系中可能与Cl-、HS-结合形成络合物或与H3SiO-4结合形成AuH3SiO4并发生迁移而形成金矿。  相似文献   

西天山中北段铜、金矿床成矿规律初探   总被引：14，自引：0，他引：14  

沙德铭  田昌烈  董连慧 《新疆地质》2003,21(2):185-189

西天山中北段地区铜、金矿产时空分布特征明显．时间上，具明显的区域性成矿特征，成矿作用集中在海西期；空间上，铜矿集中分布于赛里木微地块和伊犁晚古生代裂谷带内，金矿集中分布在裂谷带边部晚古生代中期陆相火山岩带和与板块俯冲作用相关的韧性剪切带上．铜、金成矿受含矿建造、岩浆活动和构造控制，据其成矿和分布特点划分出了5个铜矿集区和2个金矿集区，确定了3个主要成矿阶段的6种矿床共生组合，建立了区域成矿作用模式．  相似文献