| The ultramafic rock in the Ritu ophiolite Belt has been altered to serpentinite to-tally. Serpentinite is nematoblastic texture,massive structure,made of chrysotile. Met-allogenic minerals include chromite,magnetite,Penlandite and heazlewoodite.The ultramafic rocks are characterized by low CaO (0.11%-0.38%),Al2O3 (0.19%-2.06%),(Na2O+K2O) (0.0135%-0.112%) (the H2O is take off and stan-darizes),V (16.9×10-6-41.6×10-6) and high Co ( 100×10-6-150×10-6),Ni (2300×10-6-4100×10-6) and Mg# (0.86-0.90).Total rare earth element is 1.61×10-6-2.04×10-6, less than CI.The Chondrite-normalized rare earth element pat-terns are very complex,including U-type or V-type and the type depleted in light rare earth element. The rocks enrich in the strong incomatible trace ele-ments—Cs,Ru,U,delept in middle incomatible trace elements and weak incomatible trace elements—Ti,Y,compared with the PM.The petrology and the geochemistry of the Ritu ultramafic rock indicate the ul-tramafic rock is the residual mantle peridotite that have experienced complex multi-Stage,multi-period and multi-cycle evoluation or have been transformed by fluid and (or) melt in this area.The two types—MOR and SSZ of the Ritu mantle peridotite and the wide varie-ties of the Cr# in the chrome spinel indicate the mantle peridotite have experienced complex melting history.The formation process maybe have experienced two envi-ronment′s change-MOR to SSZ.The Nickel content in the Ritu ultramafic rock is high(most of them are greater than 0.2%). The Nickel in the rock mainly occurs in the Penlandite and heazle- woodite,but not occur in the serpentine.The S and Cu included in the rocks are very small,so I thinck the S and Cu are preference to the magma and be taken away.Because the Ni in the rocks is mainly included in the Penlandite and heazle-woodite and the Ni content is high ,the probability of the mineralization is valu-able.But the grain of the Penlandite and heazlewoodite is small,the washability is needed to do research more.
|
PDF Full Text Request