Mineralization characteristics and metallogenic regularity of mafic-ultramafic intrusions in Hualong area, Qinghai Province

Abstract：The ferruginous series mafic-ultramafic intrusions have Ni metallogenetic specialization, but mafic-ultramafic intrusions do not necessarily contain Ni ore. Mineralization characteristics can be used to summarize the metallogenic regularity of mafic-ultramafic intrusions and guide the regional exploration. There are 114 mafic-ultramafic intrusive bodies in Hualong area, and their mineralization characteristics and metallogenic regularity are important key factors for exploration breakthrough. The authors studied geological characteristics, geochronology and petrogeochemical characteristics of Yulonggou, Yaqu, Ashengong and Xiashentang intrusions in Hualong area, Qinghai Province, and found that the four intrusions have similar ages, focused in the range of 436Ma~449Ma, probably suggesting the products of the same tectonic setting in southern Qilian orogenic belt. S, Re-Os and Sr-Nd isotopes reveal that parent magma originated from a mantle source which had once experienced metasomatism. Its εNd(t) ratios are -7.74~+8.36, suggesting that the magma source might have been located in the asthenospheric mantle region contaminated by mantle wedge material with subduction plate metasomatism. The rich silicon strata of Hualong rocks group created the condition of assimilation and contamination for sulfide immiscibility, caused the addition of the rich silicon material, formed the sulfide immiscibility, and finally formed the different grades of magmatic Ni-Cu sulfide deposits in the Hualong rock belt, Qinghai Province. Sufficient lithofacies differentiation, enriched olivines and higher basic degree of mafic-ultramafic intrusions were favorable conditions for the formation of Ni orebodies, and could further guide the prospecting work in Hualong mafic-ultramafic intrusive rocks of Qinghai Province.