个旧老厂Sn-Cu矿床内外接触带矿体原生晕分带与深部矿体预测模型

矿床的原生晕通常形成在矿体周围,与蚀变矿物和矿石矿物同时形成。矿床原生晕的分带规律能够提供较为准确的找矿目标。一些金属矿床的原生晕具有示踪隐伏矿体的作用,从而为探测深埋矿体提供了重要的线索。老厂大型锡多金属矿床是个旧巨型锡多金属矿床的重要组成部分,以广泛发育夕卡岩化矿化为其特征。根据其空间分布夕卡岩矿化可分为两类:内夕卡岩矿化和外夕卡岩矿化。前者发生在侵入体内蚀变带,后者主要形成于侵入体附近的蚀变碳酸盐岩中。它们在地球化学特征上有以下异同:(1)内夕卡岩和外夕卡岩矿体的轴向分带序列(从矿体的头部到尾部)分别为Ag-As-Bi-Cu-F-Pb-Sn-Zn-B→Ba-Co-Cr-Ni-Sb-V→Be-Mo-W和F-B-Ba-W→Cu-Sb-Be-Cr→Sn-Pb-Zn-Ni-Ag→Co-Mo-Bi-As。这表明异常元素的种类具有高度一致性,但轴向分带序列存在很大差异。(2)统计分析表明内夕卡岩矿化具有三种主要成矿元素组合:(a)As-B-Be-Co-Sn组合代表发育在花岗岩内蚀变带的云英岩化有关的锡石-硫化物-电气石蚀变矿化组合;(b)Mo-W代表与高温夕卡岩化相关的辉钼矿-白钨矿矿化组合;(c)Ag-Pb-Cu-Zn代表后期叠加于内蚀变带角银矿-方铅矿-闪锌矿-黄铜矿矿化组合。(3)外夕卡岩矿化也具有三种主要成矿元素组合:(a)Ag-Bi-Sn-Cu代表发育在外夕卡岩带角银矿-辉铋矿-黄锡矿(锡石)-黄铜矿中低温矿化组合;(b)As-Zn-Pb代表发育在外夕卡岩带毒砂-闪锌矿-方铅矿中温硫化物组合;(c)F-Be-W-Mo代表靠近侵入体一侧萤石-绿柱石-白钨矿-辉钼矿高温矿化组合。上述表明矿化具有多期多阶段特点。最后,在原生晕轴向分带序列的基础上,分别建立了内、外夕卡岩带深部矿体预测模型,为深部成矿预测提供强有力工具。

Primary halo zonation in and a deep orebody prediction model for the inner-outer contact zone of the Laochang Sn-Cu deposit in Gejiu

The primary haloes of mineral deposits occur as envelopes around individual mineral deposits and are usually contemporaneous with mineral alteration and deposition. Zonation of primary haloes of mineral deposits is quite predictable and explicable, thus it generally provides better ore prospecting targets. Besides, primary haloes of some metal deposits may provide important insight for targeting deeply buried orebodies. The Laochang Sn-polymetallic deposit is an important member of the Gejiu giant (Sn-Cu) polymetallic deposit characterized by skarnized mineralization. The skarnized mineralization can be subdivided into endoskarn and exoskarn mineralization types based on the spatial distribution patterns. The former occurs in the inner altered intrusion zone while the latter mainly in carbonate rocks near intrusions. They have the following geochemical similarities and differences: (1) The axial zoning sequences of endoskarn and exoskarn orebodies are (from head to tail) Ag-As-Bi-Cu-F-Pb-Sn-Zn-B → Ba-Co-Cr-Ni-Sb-V → Be-Mo-W and F-B-Ba-W → Cu-Sb-Be-Cr → Sn-Pb-Zn-Ni-Ag → Co-Mo-Bi-As, respectively, indicating consistency in anomaly element but not in axial zoning sequence. (2) In endoskarn mineralization, there are three ore-forming element associations: (a) As-B-Be-Co-Sn, representing greisenized cassiterite-sulfide-tourmaline mineralization; (b) Ag-Pb-Cu-Zn, representing kerargyrite-galena-sphalerite-chalcopyrite mineralization; and (c) Mo-W, representing skarnized molybdenite-scheelite mineralization. (3) In exoskarn mineralization, there are also three ore-forming element associations: (a) Ag-Bi-Sn-Cu, representing kerargyrite-bismuthinite-stannite(cassiterite)-chalcopyrite mineralization; (b) As-Zn-Pb, representing skarnized arsenopyrite-galena-sphalerite mineralization; and (c) F-Be-W-Mo, representing greisenized fluorite-beryl-scheelite-molybdenite mineralization. The above ore-forming element associations indicate skarn mineralization involves multistage processes. Finally, on the basis of primary halo axial zoning sequence, the prediction patterns of deep orebodies in endoskarn and exoskarn zones are established, thereby providing a powerful tool for the prediction of concealed orebodies.