对豆荚状铬铁矿床成因的认识  

THE ORIGIN OF THE PODIFORM CHROMITE DEPOSITS

作　　者：周美付[1] 白文吉[1] 

机构地区：[1]加拿大达霍希大学海洋地质中心,中国地质科学院地质研究所

出　　处：《矿床地质》1994年第3期242-249,共8页Mineral Deposits

基　　金：中国自然科学基金委员会和加拿大NSERC的联合资助

摘　　要：文章提出豆荚状铬铁矿床不是上地幔局部熔融后的残余物，而是亏损地幔又经部分熔融形成的熔体发生液相不混熔，导致硅酸盐岩浆和富铬矿浆的形成。当比重不同高度分馏的熔体在上升过程发生了分离，轻熔体上升侵入于岩浆房、重熔体和铬铁矿浆，就地堆积或贯入围岩形成豆荚状铬铁矿床。豆荚状铬铁矿的伴生围岩纯橄岩，不是高度亏损的上地幔残余，可能是与铬铁矿浆伴随的一种硅酸盐熔体。与大量纯橄岩脉伴随的基性岩、超基性岩脉，也属不同程度熔融的产物。The podiform chromite deposits exhibit cumulate texture and occur in thehighly-depleted pyrolite of ophiolites.Nevertheless,they differ diametricallyfrom their host rock in origin and hence are not residues after partial melt-ing.Evidence shows that the podiform chromite deposits were formed byin-situ deposition of the upper mantle chromium一rich melt:l) accessorypicotite is obviously different from ore-forming picotite in variation trend ofchemical composition;(2) there exist mineral and silicate melt inclusions inchromite deposits; 3) their PGE patterns are similar to the PGE patterns ofstratiform chromite deposits formed by magmatic crystallization; 4)the mineralassemblage formed in the process of magmatic crystallization includes clinopy-roxene,orthopyroxene,olivine and plagioclas. Although residual picotite mightappear after partial melting, the formation of chromite deposits must have theprerequisite that the degree of partial melting should exceed 80%, but this isquite impossible in nature. There is merely a very small amount of chromiumin the initial melt, and its concentration is tliought to be the result of immi-scibility between silicate melt and chromium-rich ore magma. Light silicatemelt which might have had basaltic composition ascended to form cumulatesequences of ophiolites,whereas denser and heavier chromium-rich ore magmawas either crystallized in situ or intruded into the highly depleted pyroliteand then solidified to form podiform chromite deposits.

关 键 词：铬铁矿 成因 豆荚状 

分 类 号：P618.301[天文地球—矿床学]