Petrogenesis And Metallogenic Potential Of Zangbutai Mafic-Ultramafic Intrusion In Longshoushan, Gansu Province

The Longshoushan occur at the southwest margin of the Sino-Korea platform, which isfamous for the Jinchuan Ni-Cu sulfide deposit, one of the largest magmatic deposits in theworld. In the region of Longshoushan, there are more than20mafic-ultramafic intrusions, asthe dyke-like, vein-type or stock form, which become an important mafic-ultramafic intrusionzone.As the largest intrusion of the Longshoushan area, during60-70s, there were muchgeophysical exploration and drilling have been done in Zangbutai intrusion, but people havenot found the Cu-Ni sufild deposite. Whether Zangbutai intrusion has the metallogenicpotential? This is an important science question. This article choose Zangbutai as researchobject, through systematically researching on geology, geochemistry of the intrusion, andcomparing with the Cu-Ni sufild deposits at home and abroad, analysis the Petrogenesis andMetallogenic Potential of Zangbutai Mafic-Ultramafic Intrusion. Based on these researches we getsome understanding as follows:1. Geology sthudy show: Zangbutai intrusions comprises three periods of magmacomponents: the first mainly involve hornblendite, and become the main body; the secondintrusion is formed by Cpx-peridotite, Cpx-augite peridotite and Cpx-pyroxenolite and a littlegabbro; the last intrusion is gabbrocliabase, emplaced along the former intrusions.2. Lithogeochemical study show: The intrusions of Zangbutai have the characters ofalkaline poor, aluminum poor, and the type of rock belong to iron ultrabasic and tholeiiticseries. The REE profiles of Zangbutai intrusions are different, the first is flat, the second andthe third are LREE-enrich patterns. The trace element show Nb,Ta negative anomaly.3. Isotope geochemisty study show: the magma source region of Zangbutai intrusion isdepleted lithospheric mantle. The first intrusion had mainly undergone fractionalcrystallization of pyroxene in the magma evolution, and the second intrusion is mainlycontrolled by olivine, orthopyroxene and clinopyxene. The first and second magmasexperienced weak assimilation contamination, and the contaminated material come fromsupracrust.4. The magnetite mineralization, malachite mineralization and hematization intensiveoccur at the second intrusion. By tectonic setting, ore-forming indicator and comparing withthe Cu-Ni sufild deposits at home and abroad, we know that the second intrusion belong to thetype of magmatic sulfide deposit’s intrusion. The magnetite is formed by alteration of olivine, which has not metallogenetic potentiality, and the deep part of the intrusion may formmagmatic sulfide deposit.