蚀变岩帽的特征、成因以及在华南的分布探讨

Sillitoe（1995）蚀变岩帽（Lithocap）的定义为大范围富黄铁矿的硅化、高级泥化和泥化蚀变,在地质环境上位于古地表和浅成中-酸性岩浆侵入体之间。蚀变岩帽往往显示为突出的正地形,有助于寻找隐伏的斑岩矿化体。但蚀变岩帽在地表的范围往往多达几十个平方千米,又常常掩盖下覆斑岩矿床的蚀变矿化特征及其地球化学印记,因此大型的蚀变岩帽又给勘探工作带来一定的挑战。蚀变岩帽相关矿床的勘探需以地质填图为基础,结合近红外光谱分析（SWIR）进行蚀变填图,以及全岩地球化学以及矿物地球化学表现的元素或元素组合异常,来帮助定位热源或深部斑岩体。遥感和地球物理中的激电响应,也可以辅助定位岩体。华南地区的蚀变岩帽主要分布于长江中下游成矿带和东南沿海火山岩带。前人对安徽庐枞盆地中的矾山蚀变岩帽进行了系统研究,确定了矾山蚀变岩帽形成于白垩纪,与围岩砖桥组火山岩年龄一致。同位素和流体包裹体工作证明了形成矾山蚀变岩帽的流体主要为深部岩浆热液中的酸性气体与浅部大气降水的混合,在浅部高渗透率的火山岩及其岩性界面反应,广泛发育了一套硅化和高级泥化蚀变,指示与矾山相关可能存在斑岩和高硫型浅成低温热液铜金矿床。福建紫金山地区有中国最大的高硫型浅成低温热液矿床,主要赋存于紫金山蚀变岩帽中。紫金山蚀变岩帽的地质特征和蚀变分带已经研究的较为详细,但目前深部的侵入体还没有发现。浙江的蚀变岩帽是中国非金属矿产的重要来源,包括明矾石矿、地开石矿和红柱石矿等,这些蚀变岩帽与金属矿化的关系尚未有相关研究。根据目前的资料总结,有较多的蚀变岩帽分布在中国华南,这些蚀变岩帽特征典型,但目前的研究程度尚浅。现有的研究结果表明,华南的蚀变岩帽的成矿潜力巨大,可能存在一条巨型的斑岩-浅成低温矿床成矿带,具有广阔的找矿勘查前景,建议加强蚀变岩帽及相关矿床的找矿与研究工作。     

印度科拉尔金矿田的矿化和构造

引言世界级的科拉尔金矿田的金矿床,位于印度南部卡纳塔克邦班加罗尔东边80km处。该矿床产于科拉尔绿岩带中。该带是一条长80km、宽3—15km的太古宙上壳岩带,其大部分是由镁铁质火山岩组成。该矿床在古开矿地点上再次被发现后,这个地区自1880年以来是连续开采金矿的。从大约4800万吨矿石中回收金的总产量是790吨,被磨碎矿石的金平均回收品位为16.48克/吨。现在工厂原样品位大约是3.5克/吨,每年生产金大约1.2吨。     

The Mesoproterozoic to early Neoproterozoic passive margin Lajeado Group and Apiaí Gabbro,Southeastern Brazil

The Lajeado Group in the Ribeira Belt,southeastern Brazil,corresponds to an open-sea carbonate platform,comprised of seven overlapping siliciclastic and carbonatic formations,intruded in its upper portion by the Apiai Gabbro.These rocks have a Neoproterozoic tectonometamorphic overprint related to arc magmatism and the Brasiliano collisional orogeny.Geochronological constraints are given by new UPb SHRIMP and LA-ICP-MS data for Lajeado Group detrital zircons and for magmatic zircons from the Apiai Gabbro.The youngest detrital zircons in the Lajeado Group are 1400-1200 Ma,and constrain its maximum age of deposition to be 1200 Ma,whereas the 877 ± 8 Ma age for magmatic zircons in the Apiai Gabbro give the minimum age.Detritus source areas are mainly Paleoproterozoic(2200-1800 Ma)with some Archean and Mesoproterozoic contribution(1500-1200 Ma),with distal or tectonic stable cratonic character.The Lajeado Group should be a Stenian-Tonian carbonate platform passive margin of a continent at this time,namely the Columbia/Nuna or the Rodinia.The Apiai Gabbro displays similar age to other intrusive basic rocks in the Lajeado and Itaiacoca groups and represents tholeiitic MORB-like magmatism that we relate to the initial break-up of a Mesoproterozoic continent and the formation of the Brasiliano oceans.     

http://www.sciencedirect.com/science/article/pii/S1674987111001046

The role played by Paleoproterozoic cratons in southern South America from the Mesoproterozoic to the Early Cambrian is reconsidered here.This period involved protracted continental amalgamation that led to formation of the supercontinent Rodinia.followed by Neoproterozoic continental break-up,with the consequent opening of Clymene and Iapetus oceans,and finally continental re-assembly as Gondwana through complex oblique collisions in the Late Neoproterozoic to Early Cambrian.The evidence for this is based mainly on a combination of precise U-Pb SHRMP dating and radiogenic isotope data for igneous and metamorphic rocks from a large area extending from the Rio de la Plata craton in the east to the Argentine Precordillera in the west and as far north as Arequipa in Peru.Our interpretation of the paleogeographical and geodynamic evolution invokes a hypothetical Paleoproterozoic block(MARA) embracing basement ultimately older than 1.7 Ga in the Western Sierras Pampeanas(Argentina),the Arequipa block(Peru),the Rio Apa block(Brazil),and probably also the Paraguaia block(Bolivia).     

Zawiercia—Rzeszotar岩石圈缝合线性质的深大断裂对古生代矿化作用…

对深部岩浆和矿化现象的研究，证明了Ｚａｗｉｅｒｃｉａ－Ｒｚｅｓｚｏｔａｒ断层属于通到岩石圈下部边界缝合线性质的区域性深大断裂。断裂形成于上志留造山运动的碰撞，并把现在叫上西里西亚煤盆的段块和小波兰地块焊接在一起。断裂形成后的地质发展史看出由于焊接的不完善和愈合的薄弱，造成了裂隙的不时张开关不断发生岩浆活动和金属的矿化现象。     

在电离辐射情况下测量工作的安全保护措施

近年来地形测量队人员在电离辐射地区内作业在增加，产生的照射可能损坏设备，破坏正常的导线测量作业。现行的技术安全规定设有制定出在原子能发电站和工业企业，那些利用辐射源的地方进行测量工作时的解决问题办法。