广西大厂矿田超大型锡多金属与矽卡岩型锌铜矿床形成研究

The Dachang ore field is made up of a series of world class and large Sn-polymetallic deposits and a skarn Zn-Cu deposit, forming the rare ore association of Sn and Cu. The giant Sn-polymetallic deposits consists of stratiform ore bodies with banded structure and giant scale, high-graded ore body 100 with massive structure. Different opinions have been proposed on the genesis of the Dachang Sn-polymetallic deposits due to its complicated mineralization occurrences, therefore, new ideas and new analytical methods are needed to use to reveal the genesis of the Dachang giant Sn-polymetallic deposits. This project is going to carry out the following work: (1) analyzing the source features, the oxygen fugacity and melt exsolved volatile phases of melts of different felsic igneous rock types in the Dachang ore field; (2) revealing features of the alteration differences and micro-topography between the siliceous rocks underlying under and overlying on directly the tin-polymetallic thin layers in the stratiform tin-polymetallic bodies, respectively; (3) analyzing trace element distribution diagrams of pyrite grains from the stratiform ore bodies, ore body 100 and skarn Cu-Zn deposit; (4) analyzing H and O isotopic composition of the ore forming fluids of different style mineralization and trace element and ore forming element concentration of single fluid inclusions of minerals such as cassiterite, sphalerite, and quartz from tin-polymetallic thin layers in the stratiform ore bodies, the ore body 100, the skarn Cu-Zn ore and quartz from felsic igneous rocks in the Dachang ore field. Based on the above work, the magmatism corresponding to Cu and Sn mineralization will be revealed, the sources of ore-forming fluids and detail ore forming processes of the tin-polymetallic stratiform ore bodies and the giant scale, high-graded ore body 100 will be delineated. The key factors resulting in the giant scale and high-graded ore bodies will be proposed. The work is very important for us to understand the genesis of Dachang tin-polymetallic deposits on which different forming models have been proposed and improve our recognition level on the forming processes of giant deposits.

广西大厂矿田由一系列大型超大型锡多金属矿床及矽卡岩型锌铜矿床组成，形成世界少见的锡矿床和铜矿床组合。锡多金属矿床主要由层状矿体及100号巨型特富矿体组成；锡多金属矿床成因争论激烈，需要用新的思路和方法探讨其成因。本项目通过矿田内主要岩体岩浆源区、岩浆氧逸度及出溶流体成矿元素组成分析，层状锡矿体中锡石硫化物薄层上覆及下伏硅质岩蚀变差异及矿物颗粒微观形貌变化分析，层状矿体、100号巨型特富矿体及矽卡岩型锌铜矿体黄铁矿微量元素分布图及成矿流体单个包裹体元素组成分析以及成矿流体氢氧同位素组成分析等，探讨区内岩浆作用与锌铜矿床和锡矿床的成因关系；分析锡矿和锌铜矿床成矿流体来源及成矿过程异同，阐明层状锡矿体主要是热水沉积还是后期岩浆热液交代成因及其与锌铜矿化的关系；分析100号巨型特富矿体形成过程及关键控制因素。本工作对阐明大厂锡多金属矿床成因，提高超大型矿床研究水平有重要意义。

广西丹池成矿带大厂矿田发育大型超大型Sn-Sb-Zn-Pb矿床，也发育矽卡岩型Zn-Cu矿床。锡多金属矿床主要以似层状（91和92号）及不规则状充填巨型特富矿体（100号）产出。本项目通过丹池成矿带大厂、芒场、五圩等矿田及邻区栗木锡矿床成岩成矿年龄、大厂矿田锡多金属矿床和锌铜矿矿床Pb-S同位素组成、100号巨型特富矿体石英微结构、流体包裹体及H-O同位素组成等分析；探讨锡多金属矿床成因及形成动力学背景，阐明100号巨型特富矿体形成过程及论证锡多金属矿床与锌铜矿床成因关系。发现丹池成矿带锡多金属矿床成岩成矿时代集中于89-93Ma之间，和桂东-粤西-滇西南-越北-缅北白垩纪岩浆作用有关Sn、W及Cu矿床时代相近，形成东西向长超800公里矿带；提出矿带与古太平洋北西向俯冲无关，而与新特提斯洋北向俯冲有关；大厂矿田远离龙箱盖岩体锡多金属矿床成矿温度（300—420℃）高于相对靠近岩体拉么Zn-Cu矿床成矿温度（260-320℃），且两类矿床Pb-S同位素组成不同，加上Sn和Cu分别与还原岩浆和氧化岩浆有关，提出Sn多金属矿床和Zn-Cu矿床为不同岩浆作用产物，Sn矿体深部具有寻找花岗岩型Sn矿床潜力；发现大厂矿田100号巨型特富矿体成矿前流体从超临界至后期突然减压，结合矿体底发育隐爆角砾，成矿流体含有机质及H-O同位素组成变化大（δ18OH2O ：4.2—9.3‰，δDV-SMOW：−77 to −132‰），位于岩浆水与油田卤水之间，矿体富锡矿化花岗岩无关的Sb-Pb元素及矿体上部发育大量沥青，提出100号巨型特富矿体为花岗岩有关富Sn-Zn超临界流体在古溶洞油藏底部发生隐爆及期后与富Sb-Pb油田水混合形成的。据丹池成矿带Sn矿床年龄及栗木矿床成岩成矿年龄（211-224Ma），结合前人成果，提出广西区发育中晚元古宙、加里东期、印支期、燕山中期及燕山晚期等5期锡成矿作用。