Structural controls on orogenic gold mineralisation in the Klondike goldfield,Canada

The Klondike Schist that forms the basement rocks for the famous Klondike placer goldfield was emplaced as km-scale thrust slices in Early Jurassic time, along with some thin (10 to 30 m-scale) slices of greenstone and ultramafic rocks. Permian metamorphic fabrics in the schists were deformed during thrust emplacement by structures formed as the rocks passed through the brittle–ductile transition. Early-formed thrust-related structures were almost-pervasive recumbent folds that affected both the schist and greenstone/ultramafic slices and imposed a spaced cleavage with minor recrystallisation of micas. These structures gave way to shallow-dipping phacoidal cleavage near (within <100 m of) thrust structures. Thrust-related structures have been overprinted locally by well-defined steeply dipping reverse fault-fold zones, and associated upright folding on regional (km) to mesoscopic (m) scales. The fold-fault zones occur as two orthogonal sets of structures oriented NW to N and NE to E. Some of these steeply dipping fault zones have been reactivated by Late Cretaceous normal faulting. Orogenic (mesothermal) gold-bearing veins were emplaced in local sites of extension during or after formation of the compressional fault-fold zones and before normal fault reactivation. Over 400 veins (m to cm-scale) observed in this study imply a general NW strike for mineralised structures (W to N), but with a broad scatter of orientations. Vein emplacement was controlled principally by fold axial surfaces of kink folds of the fault-fold generation. However, some other local extension sites have opened along preexisting structures to host veins locally, including metamorphic foliation and spaced cleavage planes. In addition, irregular extensional fractures with no obvious structural control host some veins. The Klondike mineralised veins formed as swarms with broad regional structural control, but represent relatively diffuse mineralised zones, with numerous scattered small veins, compared to most orogenic vein systems. These diffuse vein swarms appear to be sufficient sources for the rich and geographically localised placer gold deposits that formed in overlying gravels during erosion of the Klondike Schist basement.     

汉寿高仑山石英岩矿床地质特征及开发前景

高仑山沉积-变质石英岩矿床产于岩坝桥岩体北东外蚀变带,是省内新型硅石矿床类型。它系灯影组硅质岩受岩体热液蚀变形成。矿石矿物成分98—99％为石英。大型矿床规模。原矿经破碎水洗法选矿后,精矿含SiO_2 99.16％,质量达优质型砂。目前产品暂应用于铸造行业,经数家精铸厂试验,能铸出合格钢铸件。该矿床开采条件优越,潜在经济价值巨大,开发利用前景广阔。     

金矿物及其赋存状态

已发现的金矿物有60余种。本文将其分为七类。在附表中列有20种较常见的金矿物及其鉴定特征。金在自然界中有三种赋存状态:可见独立矿物形式;呈次显微状于载体矿物中;或以原子状态混入其他矿物。金的工业矿物以第一种赋存状态为主,它们常与黄铁矿、毒砂、黄铜矿、磁黄铁矿、闪锌矿、方铅矿、黝铜矿和石英等连生,或以其作为载体矿物。呈次显微状的金,是以粒径小于0.2um的球粒形质点,呈机械混入物状态于黄铁矿等硫化物中。     

新疆哈密三岔口石英闪长岩体中发现锌铜矿

锌铜矿是自然界较为少见的含金矿物,以往均发现于基性——超基性岩中,在中酸性岩中发现锌铜矿,在新疆尚属首次.     

塔克拉玛干沙漠石英氧同位素与粒级关系的研究

沙漠与黄土的物源联系是黄土研究关注的问题之一。石英氧同位素可示踪物源,粒度被用以分析沉积环境,但在沙漠物源研究中将二者结合应用的报道尚不多。本文测定了塔克拉玛干沙漠沙丘沙和沙丘剖面中河湖相沉积物的粒度及不同粒级的石英氧同位素,结果显示:1沙丘沙以极细砂和细砂为主,粉砂和黏土含量很低;河湖相沉积物以粉砂和黏土为主,砂含量低于5%。2各粒级石英δ~(18)OSMOW值介于13.8‰~19.7‰,其中沙丘沙为13.8‰~19.7‰,河湖相沉积物为15.6‰~17.6‰;沙丘沙石英δ~(18)O值随粒级增大未呈现减小趋势,同一粒级石英的δ~(18)O值存在一定变异。3经比较,塔克拉玛干沙漠砂和粉砂粒级的石英δ~(18)O值均高于中国其他沙漠,且20μm的石英δ~(18)O值与黄土高原的马兰黄土、洛川黄土—古土壤序列20μm的石英δ~(18)O值并无显著性差异。     

陕西石泉北部羊坪湾金矿石英脉流体包裹体特征研究

羊坪湾金矿为陕西石泉-汉阴-旬阳金矿整装勘查区东部的一个重要的金矿,前人曾在该地区开展过大量勘探和综合研究,并取得一定的认识成果（李会民等,1997;李福让等,2009;任小华等,2015）。本次研究通过采集羊坪湾金矿中S2和S3不同期次的石英脉,对其进行流体包裹体测温研究,分析总结不同期次的石英脉包裹体特征,并对探讨其同金矿之间的关系。     

斜向波作用下海底管线周围床沙组成变化

海底管线周围的不平衡输沙影响着海底管线的局部冲刷,进而影响海底管线的安全运营。基于波浪港池实验,考虑规则波的作用,采用中值粒径为0.219 mm的原型沙铺设与波浪传播方向成45°夹角的斜坡,斜坡坡度为1∶15,研究管线局部冲刷坑床沙组成变化情况。实验结果表明:与冲刷深度随时间的发展类似,冲刷宽度随时间的发展也分为初级阶段和次级阶段;管线周围床沙粗化程度最高的地方并不在管线的正下方,而在管线的后下方;周期增加,冲刷坑床沙粗化程度增大;与原始床沙相比,周期较小时,冲刷坑下方床沙细化,周期较大时则粗化,而波高对床沙扰动的影响具有不稳定性。     

北部湾北部沉积物中石英砂表面的微结构

本文利用扫描电镜,观察了调查区现代石英砂表面的微结构。研究结果表明,在亚热带海域中的石英颗粒表面化学溶蚀痕迹最为发育。     

Integrated methodology for determining provenance of detrital quartz using optical petrographic microscopy and cathodoluminescence (CL) properties

The provenance of detrital quartz is a useful predictor in frontier basin sandstone reservoirs of the availability of coarse-grained quartz grains of plutonic or high grade metamorphic origin. The standard approach is to use scanning electron microscope (SEM) panchromatic cathodoluminescence (CL) imagery and observations from an optical petrographic microscope. We describe a work flow, modified from previous literature proposals, to determine quartz provenance in detrital grains using optical petrographic microscopy and CL properties from both a hot-cathode cathodoluminescence microscope attachment (HCMA) and panchromatic SEM-CL. HCMA analysis permits better discrimination of different types of metamorphic quartz. This method is applied to a Middle Jurassic to Lower Cretaceous section in the Bandol-1 wildcat well, located in the Laurentian sub-basin south of Newfoundland. Two types of high-grade metamorphic quartz are distinguished, one with low luminescence as described in previous literature and one with medium blue CL colour and a moderate colour shift that is also known from granulite in the hinterland. Three phases of detrital supply are identified, suggesting progressive unroofing of higher grade metamorphic sources through the middle Jurassic and major input of plutonic quartz in the early Cretaceous.     

New insights into a late-Pleistocene human occupation in America: The Vale da Pedra Furada complete chronological study

Within the framework of the studies focusing on the Pleistocene peopling of the Americas, our French-Brazilian team has undertaken a pluridisciplinary research on different archaeological sites, inside and in the neighborhood of the Serra da Capivara National Park, in Brazilian Nordeste. The present study regards an archaeological site, Vale da Pedra Furada, situated in the Piauí state in Brazil. The results of technological and functional studies suggest the existence of different successive human occupations during the Pleistocene in this region. Moreover, the geological and geomorphological studies shed new light on our understanding of sedimentary processes and confirm that the levels were not subject to any significant post-depositional processes. This is also confirmed by macro- and micro-analysis of quartz artefact surfaces. The chronological study has recently been completed employing both radiocarbon and luminescence techniques; radiocarbon dates were obtained on charcoal, multi-grain and single-grain OSL ages on sedimentary quartz grains. The results obtained with the different methods are consistent with each other: the most recent archaeological level is dated to around 8 ka and the oldest to 24 ka, indicating the open-air site of Vale da Pedra Furada to be a succession of human occupations beginning from OIS 2. These results are discussed in the context of some archaeological sites studied in the Serra da Capivara National Park of the last few decades.