岩浆通道成矿系统

全球最主要的岩浆铜镍硫化物矿床基本特征是:(1)矿石与围岩边界平直,呈侵入接触关系;(2)"矿浆"在岩浆成矿系统的晚期上侵就位;(3)矿体赋存于岩浆通道中.已有的成矿模型不能同时解释这三个基本特征,暗示必须进一步理解岩浆铜镍硫化物矿床的形成机制.最近几年我们的研究发现岩浆铜镍硫化物矿床中典型矿石具有如下特征:(1)矿石中存在流体晶矿物组合,它们既不同于岩浆岩中的矿物组合,也不同于变质岩中的矿物组合,推测是从流体中直接结晶的产物;(2)铜镍硫化物矿床中不同部位矿体中矿石存在显著的成分变化,前锋端矿石以富Ni为特点,尾端矿石富含Cu、Pt、Pd.据此,本文提出了"岩浆通道成矿系统"的新模型,试图整合解释岩浆铜镍硫化物矿床中的各种观测事实.所谓岩浆通道成矿系统,系指岩浆演化晚期,"矿浆"运移和就位的空间及其相关成矿要素的组合.该模型强调:(1)深部岩浆房在岩浆矿床的形成过程中起着非常重要的作用,"矿浆"定位于岩浆成矿系统演化的晚期;(2)矿浆具有整体的流动性,因而提出了"岩浆通道前进方向"的概念;(3)所谓的"矿浆"实际为富含矿熔体-流体流,后者因失去挥发份而呈"矿浆"状,以大的流体体积和流体/熔体比值为特征.数值模拟表明,往硫化物矿浆加入挥发份流体可以显著提高矿浆的上升能力.当加入的挥发份流体达到30vol.%时,受到质疑的密度问题将不复存在,矿浆具有快速上升到浅部地壳的能力.但是,如此富含挥发份的矿浆也不再是传统概念上的矿浆,而是含矿熔体-流体流.此外,由于流体超压等原因,含矿熔体-流体流利用先存的构造薄弱面快速上升,形成岩浆通道,并在有利的部位卸载成矿金属形成矿体.因此,矿体常常侵入切割围岩.

Magmatic Conduit Metallogenic System

The primary characteristics of the key magmatic Cu-Ni sulfide deposits in the world are: (1) There is an obvious boundary between orebodys and country rocks, and orebodys always intruded into country rocks; (2) "sulfild melts" migrate and settle in the later stage of magma evolution; (3) all orebodys settle in the conduit of magma. Until now, no models of magmatic deposits' origin can explain all these characteristics of magmatic Cu-Ni sulfide deposits. It infers that new model is needed to depict the Cu-Ni sulfide deposits's origin. Our recently research shows that (1) there are Fluid Minerals Assemblages in the sulfide ores, this implies that there are a lot of fluid in the ore magma when it crystallized; (2) the composition of ores in different parts in the Cu-Ni sulfide deposits is different. The ores are richening in Ni in the front of magmatic conduit, and richen in Cu, Pt, Pd in the back of magmatic conduit. A new model "Magmatic Conduit Metallogenic System" is advocated by the authors. The definition of "Magmatic Conduit Metallogenic System" is the space of migration and settlement of melt-fluid flow bearing metals in the later stage of magma evolution in the magma metallogenic system. There are very complicated structures in the "Magmatic Conduit Metallogenic System". There are three points are important compared with "Magmatic Conduit Metallogeny". (1) The deep magmatic chamber plays a very important role in the magmatic deposits' origin, "ore magma" migrate and and settle in the later stage of magma evolution; (2) "ore magma" moves as a whole, and the concept of moving direction of magmatic conduit is advocated; (3) "ore magma" maybe contain a lot fluids, it belongs to melt-fluid flow bearing metals. After degasing, "ore magma" settles as orebodys. Numerical modeling shows that 30% fluids are added into "ore magma", the density of "ore magma" will dramatic decrease, and it can move upward easily. Because of the fluid overpressure, melt-fluid flow bearing metals will move along the structure weakness (for example boundary of two kinds of rocks and faults), so ores always intruded into the country rocks in the magmatic sulfide deposits.