Timing of Fracture Formation and Duration of Mineralization at the Hishikari Deposit, Southern Kyushu, Japan

Abstract. The Hishikari epithermal gold deposit consists of the Honko-Sanjin zone and Yamada zone. On the basis of observed crosscutting relationships of veins, vein system in the Hishikari deposit was classified into the early and late veins. They differ from orientation, width, control by unconformity, the amount of displacement and structural features, but have similarity in gold grade and Au/Ag ratios. K-Ar ages are presented for the classified veins to clarify timing of fracturing and duration of mineralization.
Age determination revealed that the early veins in the Honko-Sanjin zone range from 0.86 to 1.11 Ma and that the late veins range from 0.73 to 0. 84 Ma. The economically most important mineralization in the Hishikari deposit occurred around 0.90 Ma in a very short period (about 0.05 million years).
The distribution of mineralization age in the whole Hishikari deposit, occurrences of slickensides and ground water temperatures imply that mineralization lasted longer in the southern part of the deposit. As compared the early veins with late veins, structural changes including width, strike, dip and vein characteristics occurred at around 0.85 Ma.     

Crystal-rich mass flow deposits related to the eruption of a sublacustrine silicic cryptodome (Early Permian Collio Basin, Italian Alps)

Sedimentological, granulometric and petrographic data are presented from a detailed study on a crystal-rich mass flow deposit, which is presumably related to the eruption of a sublacustrine cryptodome. The deposit forms a prominent intercalation in the Lower Permian Collio Formation in the Italian Alps north of Brescia. Outcrops of the 10–20-m-thick volcaniclastic deposit (Dasdana I Beds, DB) can be traced over 12 km from east to west. The DB consists of a thick, crystal-rich, sandy–gravelly lower subunit representing a sequence of amalgamated Bouma-a(b) divisions overlain by a thin, well-bedded, sandy–muddy subunit that is rich in outsize porphyritic silicic fragments. Modal and computer-aided image analyses reveal that the crystal-rich lower subunit contains up to 80% of volcanogenic crystals. Some samples contain up to 60% of porphyritic fragments, which have a phenocryst content of about 20%. The wide textural range from cryptocrystalline, poikilomosaic, to rarer medium-grained granophyric groundmass, the irregular to lensoid shapes of the porphyritic fragments, and the presence of basement and sedimentary clasts suggest that the DB originated from a sublacustrine eruption of a partially extrusive cryptodome (ca. 1.6 km³). Two other porphyritic felsic cryptodomes (Dosso dei Lupi, Dosso del Bue), described briefly here, emplaced into the Collio Formation sometime after the DB event, and expose flat bases and tilted sediments at their sides. Textures observed in these domes are comparable to those found in the DB porphyritic fragments.     

Enrichissement en uranium authigène dans les sédiments glaciaires de l'océan AustralEnrichments in authigenic uranium in glacial sediments of the Southern Ocean

Four sediment cores from the Polar frontal zone and the Antarctic zone in the Indian sector of the Southern Ocean present an increase of authigenic uranium during glacial periods. We show that this increase in uranium is due to a combination of (i) an increase in the lateral transport of organic matter, (ii) a decrease in the oxygen in deep waters, and (iii) a process of diagenesis. It appears that uranium concentration cannot be used as a proxy of palaeoproductivity in the Southern Ocean, as previously suggested by Kumar et al. in 1995. To cite this article: L. Dezileau et al., C. R. Geoscience 334 (2002) 1039–1046.     

塔里木盆地西部含盐系地层成盐元素的地球化学初步研究

钾矿是我国目前紧缺的矿种之一 ,钾矿的寻找对我国有着十分重要的意义。塔里木盆地是我国第三系地层的广泛发育区域 ,有一定的找钾远景 ,尤其是库车、莎车等地区。通过对塔里木盆地 (坳陷 )西部的区域地质概况、成矿条件等的介绍 ,运用地球化学的分析测试手段 ,对塔里木盆地西部采集到的样品作了地球化学分析。论述了该区成盐沉积的地球化学特征 ,并讨论了该区形成钾矿的可能性。     

从江县翁浪金矿床容矿岩石与围岩蚀变及其找矿标志

文章简单介绍了构造蚀变岩型金矿翁浪金矿床的容矿岩石和围岩蚀变特征，指出该类矿床的找矿标志，对进一步寻找此类矿床有一定的意义。     

宁芜地区大平山铜矿、天台山黄铁矿与古火山机构关系的探讨

以大平山铜矿、天台山黄铁矿矿为例，阐述了该区的矿区、矿床地质及火山机构特征，并从成矿时间、空间及成因三个方面论述了矿床成矿与古火山机构的关系。     

锡铁山铅锌矿地质特征、矿床成因及找矿标志

通过找矿工作的实践，认为锡铁山铅锌矿床是由火山喷流沉积—后期热液叠加改造富集的块状硫化物多金属矿床。区域上NW—SE向早古生代形成的裂谷带，三级盆地内沉积的晚奥陶世滩间山群的大理岩与绿片岩系是表区找矿的最佳区段。而绢云绿泥斜长片岩、含碳质绢云绿泥片岩、白色大理岩、条带状大理岩是铅锌矿的最重要的找矿标志。     

叶蜡石传压介质资源初步研究

分析国内叶蜡石传压介质材料供需状况，指出北京赵家台叶蜡石传压介质材料资源枯竭，虽然国内叶蜡石矿石资源丰富，但适宜作叶蜡石传压介质材料资源却极少，急需从资源和材料特性着手，加大研究力度，寻找新的接替资源。     

阿尔泰可可塔勒铅锌矿床围岩蚀变及成因

可可塔勒铅锌矿床受火山喷发中心和沉积洼地控制，铅锌沉淀于海进阶段的局限还原卤水池中；矿下存在大型蚀变带，构成成矿流体对流循环过程中的水-岩作用带；后期造山挤压过程使地层和矿体倒转，矿床最终定位于麦兹倒转向斜之北东倒转翼的东南近转折部位。指出该矿床属海底火山喷流沉积改造型块状硫化物铅锌矿床。     

层控夕卡岩型矿床成矿系统的元素活动性及质量迁移--以铜陵冬瓜山铜矿床为例

应用改善了的质量平衡方程研究冬瓜山层控夕卡岩型铜矿床成矿系统的元素活动性及质量迁移，结果表明：系统中Zr,Hf,Y和Nb为不活动元素，其余均为活动元素。主量元素中仅CaO为迁出组分，其质量迁移量为84％，其余均为带入组分，带入量最大的SiO2的质量迁移量高达2384％；稀土元素均为带入组分，其中，中稀土较轻稀土和重稀土的活动性更强；其它微量元素中，带入序列由强到弱为：Cr→Ta→Sn→Th，迁出序列由强至弱依次为：U→Sb→Ni—Sr→Ba→Bb→Co→W；成矿元素Cu和Ag为带入组分，其中Cu的带入量最大，质量迁移量高达1200％。本文还得出两点具普适性认识：①稀土元素较其它微量元素对体系条件的变化更为敏感，且往往表现出明显的规律性变化，能更好地示踪地质地球化学过程。②不同元素在不同体系中的行为特征差异极大，仅凭经验判定某一元素为不活动元素往往不可靠。因此，在开展质量平衡研究时，首先采用适当方法确认体系的不活动元素是一项不可或缺的前提工作。