Tectonic settings discussion of magmatic nickel−cobalt sulfide deposits in the eastern Kunlun orogenic belt

This paper is the result of mineral exploration engineering.

Objective The Xiarihamu giant magmatic nickel−cobalt sulfide ore deposit in the eastern Kunlun orogenic belt, the largest magmatic nickel−cobalt sulfide deposit discovered in orogenic belt in the world, is the world's largest prospecting breakthrough in the magmatic sulfide deposits area in the past twenty years after the discovery of the Voisey's Bay deposit in Canada. In addition, several large−scale magmatic nickel−cobalt sulfide deposits, such as Shitoukengde, were discovered, indicating enormous prospecting potential in the eastern Kunlun orogenic belt.

Methods Accurate zircon U−Pb dating found that the ore−bearing mafic−ultramafic rocks in the eastern Kunlun orogenic belt formed at 425−330 Ma. The ore−bearing mafic−ultramafic rocks are distributed along the north Kunlun fault and the central Kunlun fault. The ore−bearing mafic−ultramafic rocks reflected a large−scale magmatism event.

Results The lithofacies of these ore−forming rocks are mainly dunite, pyroxene peridotite, and pyroxenite. The SiO₂, MgO, Al₂O₃, and CaO content ranges from 31.52% to 53.31%, from 7.5% to 39.03%, from 0.1% to 16.01%, and from 0.23% to 13.85%, respectively. On the Harker diagram, the MgO content is negatively correlated with SiO₂, Al₂O₃, Na₂O, and K₂O, respectively. The total amount of rare earth elements is between 6.36×10⁻⁶ and 81.5×10⁻⁶, with an average of 29.92×10⁻⁶. The average LREE/HREE, (La/Sm)_N, (La/Yb)_N, (Sm/Nd)_N, (Gd/Yb)_N value is 5.34, 2.58, 5.99, 0.76, and 1.78, respectively, indicating the degree of differentiation between light and heavy rare earths is high. On the primitive mantle−normalized trace element spider diagram, the ore−bearing mafic and ultramafic rocks have a relatively uniform distribution curve, which are characterized by depletion of high field strength element (Ta, Nb, Ti, and P) and enrichment of large−ion lithophile elements (Rb, Th, and U). The Sr and Nd isotope data indicate that the magma source areas of the Xiarihamu ultramafic intrusion and the Shitongkengde ultramafic intrusions were derived from the asthenosphere mantle. The δ³⁴S value shows a high positive value, revealing that crustal−sulfur contamination played a great role during sulfide saturation.

Conclusions Based on the regional tectonic evolution, we believed that the magmatic nickel−cobalt sulfide deposits in the eastern Kunlun orogenic belt are associated with the break−up of the Paleo−Tethys Ocean. This opinion is significant to the ore−forming theory of magmatic nickel−cobalt sulfide deposits in the orogenic belt and could guide the regional exploration of the magmatic nickel−cobalt sulfide deposits.