广西西大明山罗维矿区层状矽卡岩的发现及成矿意义

Discovery of strata-bound skarns and mineralization significance in Luowei mining area,Xidamingshan,Guangxi

罗维矿床位于广西西大明山复式背斜东端,是一个新近探明的中-大型钨铋多金属矿床。通过钻探,在矿区深部发现了一套产状非常稳定的矽卡岩层,此套矽卡岩并非发育在岩体与地层的接触带,而是分布在远离隐伏岩体400~550 m的寒武系小内冲组地层内。该矽卡岩层在垂向上至少发育7段,与地层交互发育,单层厚度从数十厘米到数米不等,形成稳定的层状或似层状形态。矽卡岩的内部分带非常明显,从中心到边部依次出现绿帘石石榴子石矽卡岩、石榴子石辉石矽卡岩、辉石矽卡岩和斑点状角岩。矽卡岩矿物主要为石榴子石、辉石、角闪石、绿帘石和绿泥石等矿物组合,且在矽卡岩中赋存着白钨矿、辉铋矿、磁黄铁矿、黄铁矿、方铅矿、闪锌矿和辉钼矿等大量的金属矿物。电子探针分析表明,矽卡岩中的石榴子石以钙铝榴石(Gro=71%~89%)为主,而辉石则为透辉石(Di=47%~75%)类型。研究认为,罗维矿区的矽卡岩属于钙质矽卡岩,矽卡岩矿物中的Fe^(2+)/Fe^(3+)值(Fe^(2+)/Fe^(3+)=0.03~1.05、K_p=1.72~4.82)指示了成岩期属于一种较强酸性的还原环境。此外,罗维矿区矽卡岩的矿物化学组分特征与全球典型的还原型含钨矽卡岩具有良好的类比性,指示了矿区具有良好的钨矿勘查潜力。

Luowei mining area,a newly discovered middle-large tungsten-bismuth polymetallic deposit,is located in the east of Xidamingshan antclinorium of Guangxi. During the drilling work,a set of stable skarn was found laying in deep position of the mining area. This set of skarn was not developed in the contact-belt between the intrusion and strata,but distributed at 400- 550 m away from the concealed intrusion. Skarn layers have at least 7 segments in vertical,and all interbed with the strata with each single layer ranging from tens centimeters to several meters,showing a stable strata-bound and stratoid form. The inner part of the skarn can be divided into epidote-garnet skarn,garnet-pyroxene skarn,pyroxene skarn and mottling hornstone laying ordinarily from the center to the edge. Petrographic study found that the skarns mainly contain garnet,pyroxene,hornblende,epidote and chlorite and other mineral compositions. Plenty of scheelite,bismutinite,pyrrhotite,pyrite,galena,sphalerite and molybdenite occurred in the skarns. Electron probing analyses show that part of garnet in the skarn is mainly the grossular（ Gro = 71%- 89%）,and pyroxene as the diopside type（ Di = 47%- 75%）.Studies suggest that the skarn of Luowei mining area belongs to the calcic type. The Fe^（2＋）/ Fe^（3＋）ratio（ Fe^（2＋）/ Fe^（3＋）= 0. 03- 1. 05,K_p= 1. 72- 4. 82） indicates that the diagenesis stages belong to a kind of strong acid reductive environment. In addition,the mineral chemical composition of Luowei skarn is similar to the global reduced type tungsten bearing skarn,which indicates a good potential for further tungsten exploration in this area.