内蒙古流沙山金(钼)矿床地质特征及矿床类型的划分

流沙山矿床是近年来在内蒙古西部发现的一处金 (钼 )矿床。金 (钼 )矿化主要在海西期花岗闪长岩内呈大脉细脉和线脉产出 ,其空间展布形态受一系列环状断裂带控制。金 (钼 )矿体多为环状到半环状透镜体 ,局部地段为扁豆群和楔状体。矿石的金属矿物有辉钼矿、白钨矿、辉铋矿、黄铜矿、黄铁矿、钼钙矿、自然金和银金矿。脉石矿物有石英、钾长石、斜长石、黑云母和角闪石 ,其中辉钼矿Re Os同位素等时线年龄为 (2 6 0±10 )× 10 6a。矿体的围岩蚀变主要有硅化和钾化 (钾长石化和绢云母化 ) ,次为绢英岩化和青盘岩化。本文重点研究了与矿化有关的花岗岩类岩相学和岩石化学 ,阐述了金 (钼 )矿床的矿化特征 ,划分了矿床的蚀变分带。在对比流沙山金 (钼 )矿床与国内外经典性斑岩型金属矿床主要特征的基础上 ,将流沙山 (钼 )矿床确定为深成岩型斑岩金 (钼 )矿床

GEOLOGICAL FEATURES AND METALLOGENIC TYPE OF THE LIUSHASHAN GOLD(MOLYBDENUM)DEPOSIT IN EJIN QI (PREFECTURE),WESTERN INNER MONGOLIA

The newly discovered Liushashan Au (Mo) deposit in Ejin Qi (Prefecture), western Inner Mongolia, is hosted by a Hercynian volcanic intrusive complex located along the northern margin of the Kazakhstanian Beishan paleo plate. Gold (molybdenum) mineralization occurs within the Hercynian Liushashan granodiorite stock as quartz K feldspar veins, quartz veins and Au (Mo) bearing stockworks, and is controlled by a number of ring type fracture or fault zones. Individual veins and stockwork systems can be traced along strike for 115 to 1000 m, and downdip for 250 to 400 m; they range from 4 to 12 m in thickness. Alterations around the Au (Mo) bearing veins and stockwork systems are mainly silicification, K feldspathization, sericitization, pyritization, carbonatization and chloritization. The width of the alteration zone ranges from 0.1 to 10 m. Among them, the silicification and K feldspathization are closely associated with Au (Mo) mineralization.The mineralogical composition is relatively simple. It is composed of molybdenite, scheelite, bismuthinite, chalcopyrite, pyrite, powellite, native gold and electrum. Gangue minerals include quartz, K feldspar, plagioclase, biotite, and hornblende. Ore grade averages 5.4×10 -6 Au, 0.24×10 -2 Mo and 0.40×10 -2 WO 3. Native gold is generally coarse grained and visible in hand specimens. Re Os isotope data for seven molybdenite separates defined a correlation line corresponding to an age of (260±10)×10 6 a, which is close to the K Ar hornblende isotopic ages (261×10 6-262×10 6 a) of the Liushashan granodiorite stock. The combined geochemical data, isotopic ages and petrological observations indicate that the Liushashan deposit belongs to plutonic type porphyry Au (Mo) deposits. It is believed to be a product of Hercynian igneous process along the northern margin of the Kazakhstanian Beishan paleo plate. Meanwhile, the genetic model and mineral exploration criteria of the Liushashan deposit can also be used as useful tools during the comprehensive evaluation of concealed precious metal deposits in the Beishan area, western Inner Mongolia.