华北地台北缘成矿带大青山绿岩型金矿地质特征

本文详细阐述了大青山地区绿岩型金矿的地质特征和找矿标志,指出金矿化带赋存在二道洼群大理岩与其它岩层的接触部位,同时受韧性剪切带控制,在大理岩褶曲部位或下层位有利于形成较富矿体。该类型金矿的发现,大大地拓展了在大青山地区的找矿空间。     

Gold Occurrence and Ore Genesis,Yata Micro—Disseminated Gold Deposit,Guizhou,Southwest China

The mode of occurrence of gold in the Yata micro-disseminated gold deposit is ap-proached through chemical phase studies coupled with ore-dressing monitoring and micro-beam analysis.The results showed that gold occurred for the most part as ultra-microscopic particles adsorbed on the surfaces or fracture planes of pyrite and other sulphides.The proportions of gold of different occurrences were estimated solutions containing nanometer-sized gold particles were prepared following the hydrolysis-reduction procedure and the adsorption of nanometer-sized gold on ordinary sulphides and rocks was experimentally determined.It is evident that sulphides are good adsorbents of gold and this is consistent with geological observations.     

Geochemical Studies of Sodium Enriched Metavolcanite Series in the Area of Longbohe Copper Deposit,Yunnan Province,SW China：Nd,Sr and Pb Isotopic Characteristics and Chronology

The chronological data obtained by a variety of dating methods have confirmed that the sodium enriched metavolcanite series in the area of the Longbohe copper deposit at Jinping, Yunnan Province, was formed during the Proterozoic (its Pb−Pb isochron age=1595±75 Ma), corresponding to the Dahongshan Group sodium enriched metavolcanites. The Sm−Nd isochron age of 1336±46Ma should represent the time at which this series of volcanic rocks experienced spilitization in response to sodium metasomatism, equivalent to the time of sedimentation of the Ailaoshan Group and Yashan Group rocks. The Rb−Sr ages of the volcanic rocks and the Pb−Pb ages of copper ores have recorded the events of strong dynamic metamorphism and of strong reworking-metallogenesis of copper during the Jinningian period. Similarities in forming age, rock assemblage and isotopic characteristics between the sodium enriched metavolcanite series and the Dahongshan Group sodium enriched metavolcanite series have provided new clues to the exploration of the Dahongshan-type copper deposits in this area. Granted jointly by the National Natural Science Foundation of China (Nos. 49702022, 40073001) and the State 973 Program (No. G1999043215).     

玛曲县格尔柯金矿床控矿地质条件及其矿床成因探讨

格尔柯金矿 (即大水金矿 )是产于西秦岭南带西倾山—迭山逆冲褶断带南缘的特大型金矿。矿床控矿地质条件为构造单元界断裂带、深源浅成花岗闪长斑岩小侵入体、下三叠统马热松多组 (T1m)碳酸盐岩沉积建造 ,与金矿关系密切的矿化蚀变有硅化、赤铁矿化、褐铁矿化和方解石化 ;矿床成因类型为层控—热水溶滤构造蚀变岩型。     

甘肃小柳沟钨多金属矿地质特征及成矿模式

小柳沟钨多金属矿于 90年代初发现 ,目前已具大型、超大型规模。共有 4个矿床。成矿主要与长城系朱龙关群和隐伏花岗岩有关。该矿床成矿物质来源具双重性 ,成矿温度为中高温 ,成矿流体为中等盐度 ,同位素计算模式年龄确定其成矿于加里东期。矿床成因属于火山喷发沉积—岩浆热液改造矿床。     

山东省胶莱盆地东北缘宋家沟金矿地质特征及其成因初探

山东省宋家沟金矿位于胶莱盆地东北缘 ,产于莱阳群林寺山组断裂破碎带中。牟—即断裂带为切割莱阳群的断裂 ,对金矿起控制作用。早白垩纪晚期的火山—岩浆活动为深部含金热液的运移提供了通道 ,并在其有利的构造部位沉淀成矿。稀土元素特征和氧、硫同位素特征亦说明宋家沟金矿的物质来源以深源为主 (幔源及下地壳中的金 ) ,是早白垩世晚期的火山—岩浆活动作用的结果。     

中条山同善天窗铜矿类型及找矿新认识

在总结同善构造—剥蚀窗内成矿地质条件的前提下 ,运用成矿系列理论 ,把区内具有多种表现形式的变基性火山岩型、变砂岩型、大理岩型三大类铜矿分成了八种亚类 ,认为诸类铜矿与区内广泛发育的新太古代基性岩存在着成生联系 ,铜矿的形成经历了一个复杂的过程。早期的海底火山喷发带来的铁、铜、硫等成矿物质 ,经过最初的海水富集、火山活动末期的热液作用富集以及后来区域变质叠加富集进而形成了这一系列矿床。同时提出了新的找矿思路、找矿方法及找矿靶区。     

华北陆块北缘西段中元古代与裂谷作用有关的铁、稀土、多金属矿床特征及成因

华北陆块北缘西段狼山—白云鄂博裂谷系中元古代形成的大型多金属矿床 ,是我国重要的铁、稀土、铜、铅、锌矿产地。矿床为产于沉积岩中热水沉积型多金属矿床。其形成受地层、构造控制 ,与裂谷作用有着密切的关系。裂谷系内外分支的地质环境及矿床矿种不同 ,导致矿床特征及成因具有一定差异。白云鄂博铁、稀土矿床为钾、钠、磷等含量较高的热水沉积型 ,霍各乞铜、铅、锌多金属矿床为与中基性火山岩有关的过渡热水沉积型 ,东升庙和甲生盘等铅、锌多金属矿床为热水沉积型。文中将对上述矿床分别进行论述。     

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.