Petrogensis Of Magnesian Rocks Of Paleoproterzoic And Their Ore-control Role On Borate Deposits In East Liaoning

East Liaoning borate deposits are special metamorphic-hydrothermal~metasomatic borate deposits and are distributed in "Liaoji paleorift" of Paleoproterozoic of China. Their rocks boron-bearing are Lieryu formation of Liaohe group which went regional metamorphism with amphibolite facies, and their host rocks are magnesian rocks such as magnesium peridotites, olivine basalts and magnesian marbles.The special suite of magnesian rocks (magnesium peridotites, olivine basalts and magnesian marbles) is the product of liquating and erupting of magnesian magma in the intermediate stage of development of "Liaoji paleorift" .The three kinds of magnesian rocks are distributed limitly in lentoid , layer-like , and contained each other. They are maded of magnesian minerals and are of textures and structures of igneous rocks. Their characteristics of major elements are magnesian-rich , magnesium peridotites display characteristics of last phase of mantle peridotites melting partly, olivine basalts display characteristics of weak alkali basalts , and magnesian marbles display some characteristics of magmatic carbonatites . Their trace elements are similar to igneous rocks' . Ttheir REE elements are of similar La/Yb value, the REE elements of magnesium peridotites and olivine basalts display that their formed setting are similar (from tholeiite to alkali-basalt), and the REE elements of magnesian marbles between the REE elements of chondrite and sedimentary rocks. The composition of C-O isotopes of the magnesian marbles can indicate that the rocks are of characteristics of magmatic origin.The suite of magnesian rocks is not only the host rocks of east Liaoning borate deposits, but also has decisive role on forming of borate deposits:(1)the borate ore bodies and magnesian rocks are same in stratigraphic position, and their shape controlled by attitude of magnesian rocks;(2) ores have relationship of replacement and inheritance with magnesian rocks in composition and shape of minerals, texture, structure ,etc.;(3) major elements are of succession , trace elements are similar and characteristics of evolution of REE elements are accordant between ores and their host rocks, specially, the patterns of REE elements indicate that the formation of ores are depended on magnesian rocks and migmatization.The metallogenic model of east Liaoning borate deposits can be divided into two courses, the one is initial enrichment of boron in original ore-source layer (volcanic eruption— sedimentation) , the other is replacment of hydrotherm boron-bearing on magnesian rocks inregional metamorphism and migmatization, specially, the later one, it favored the final formation of east Liaoning borate deposits, in this course, a large of hydrotherm is formed in regional metamorphism and migmatization , the hydrotherm makes boron activate, and the hydrotherm boron-bearing is formed. As result, the magnesian borate type ores, which are distributed only in east Liaoning borate deposits, are formed with replacing of hydrotherm boron-bearing on magnesian rocks and boron silicate rocks tourmaline-rich are formed with replacing of hydrotherm boron-bearing on aluminous silicate rocks. The formats that the hydroherm boron-bearing act on magnesian rocks are filling and metasomatism.