安康牛山火山岩区基础地质及金银铜的成矿条件

A RESEARCH ON SOME BASIC GEOLOGIC PROBLEMS,GOLD-SILVER-COPPER MINERALIZATION CONDITIONS AND PROSPECT OF NIUSHAN MOUNTAIN VOLCANIC ROCK DISTRICT,ANKANG CITY,SHAANXI PROVINCE

安康牛山地区的海相火山岩构成安康隆起的主体。经两年的研究取得了如下认识和成果:①火山岩岩石学、岩石地球化学研究表明,郧西群火山岩可分为上、下两个岩性段,岩石类型计有石英角斑岩、钾石英角班岩及其同质火山碎屑岩;耀岭河群为细碧岩、钠长辉绿岩及其同质火山碎屑岩,火山岩组合为石英角斑岩-细碧岩,缺失中性角斑岩类,前者为钙碱性系列,后者为拉斑玄武岩系列,含钙碱性系列分子。火山岩具双模式特点,为裂谷环境产物。加里东晚期或华力西早期侵位的酸性侵入岩为岛弧环境产物。②首次研宄并划分出七条韧性剪切带,在空问上呈近南北,和南东-北西两组方向,推测其为共轭韧性剪切带组合。③论述了恒河以东,付家河以西地段的线性构造和环形构造,并在此基础上论证了猴子崖-牛山主峰一带为一大型构造穹窿。④本区火山变质岩的变质矿物有七种组合类型和两个变质相。⑤本区首次发现了高压变质相系的蓝片岩(钠钙闪石绿片岩)。这对阐明安康隆起、平利降起,乃至整个秦岭造山带的构造演化具有重要的大地构造意义。⑥基于Ma区和Pan区铜银矿点和矿化地段的发现和金银铜矿化特征、成矿条件的分析,初步认为本区已知的火山热液脉型和火山变质热液脉型铜矿不具备形成工业矿床的地质条件,金矿产成矿因素较为复杂,其成矿前景尚欠明确,银矿产尚有一定的成矿潜在前景。笔者等确立的找矿指导思想是以银为主的金银铜综合找矿。

Marine volcanic rocks of Niushan mountain which lie to the northwest of Ankang City and north of Yuehe River, Shaanxi Province, make the main part of Ankang rise. Several advances have been made in basic geology research and gold-silver-copper prospecting after two year's study: ①Researches in petrology and geochemistry of volcanic rocks indicate that Yunxi Group may be devided into upper and lower lithologic sections of which the rock type consists of quartz-keratophyre, potassic quartz-kerato- phyre and their pyroclastic rocks; that Yaolinghe Group consists of spilite, albite-diabase and their pyroclastic rocks. Volcanic rock association is made up of quartz-keratophyre-spillte. Keratophyre is absent. Yunxi Group belongs to calkaline series while Yaolinghe Group to tholeiite series containing rocks of calkaline. Thus the rocks are characterized by bimodel association and are the products of rift magmatism. Acid intrusions of Late Caledonian or Early Variscian Epoch result from island arc magmatism. ②The exist of ductile shear zone in Niushan mountain area has been studied and demonst- rated for the first time. Seven shear zones which spatialy strike N-S or SE-WS are discovered and inferred to be possibly conjugate zones. ③By the means of satellite photo explanation and field research, linear and annular structures lying to the east of Henghe River and the west of Fujia- he River are demonstrated, and on the basis of which that Houziya cliff to Niushan peak zone to be on a large scale a structural dome is discussed. ④Studies in volcanic metamorphic rocks and type metamorphic minerals indicate that there are seven metamorphic mineral associations in the area, and upon that the volcanic metamorphic rocks are derided into hight and low greenschist facies. Besides, sodic-calcic-amphibole greenschist facies belonging to low temperature and high pressure which develops at certain position are also devided. ⑤Blue schist(sodic-calcic-amphibole greenshist) of high pressure metamorphic facies series has been discovered for the first time and this is of great significance to clarify tectonicaly the evolution of Ankang rise, Pingli rise, even that of the whole Qinling orogenic belt. ⑥On the basis of the discoveries of Ma copper-silver occurence and Pan mineralized district and the analysing of gold-silver-copper mineralization characteristics and conditions, it is considered that preliminaryly copper deposits in the area known for volcanic hydrothermal soluton type and volcanic metamorphic solution type have no geologic conditions to form those for industral aid. The factors controlling gold mineralization are com- plexe and the prospect of which is indistinct. However, sider is to some extent potential. On the basis of above, guiding thought in mineral prospec- ting at this area is established as taking silver as the key for gold-silver- copper comprehensive prospecting.