西藏铬铁矿基本特征及其成因模式探讨

西藏铬铁矿分布于两个基性超基性岩带上,受板块结合带控制。赋存铬铁矿的岩体无根、与围岩呈断层接触、是板块构造侵位的残体。铬铁矿及赋矿岩石在上地幔形成。成岩成矿机制为地幔岩的局熔改造作用,故属地幔成因。

ON THE BASIC FEATURE AND ORIGIN MODEL OF CHROMITE IN XIZANG

Mineral reserves of chromite in Xizang takes the first place in China, and the largest mineral deposit of China is in Xiang. The former studies are of low degree and the explored mineral reserves of development of industry of chromite in Xizang can not meet the needs of development of industry of China. Being most associated with nickels (Ni) and platinum metals, chromite in Xizang may be syntheticaly utilized to increase the economic valus. Understanding the origin of mineral deposit is of important significance for both looking for and exploring mineral reserves. At present chromite origin with the distribution can be classified into three types, namly magmatic origin, metasomatic origin and mantle origin. Mantle origin is used to discuss chromite in this paper. Rock bodies bearing chromite, being without roots and contacting with country rock by fauts are the remnants controlled by suture zone of plate tectonic. The dispersive mineralization elements in upper mantle were seperated from pyrolite by "partical melting and reforming" to form Cr-spinels, which selectively gathered in shear areas during the course of mantle convection and moved to from chromite bodies. Therefore, chromite is the highly partical melting extreme remnant, rich in Cr and Mg. This is the principal distinction of origin mechanism between chromite of pod type and general iron rich magmatic ore. The later is mineralization of chromite derived from pyrolite, which was emplaced to present states by plate tectonics.