GEOLOGICAL SETTING AND PROSPECTING DIRECTION OF COBALT-NICKEL MINERALIZATION IN LIAONING-JILIN TECTONIC BELT

The paper focuses on the prospecting of cobalt-nickel deposits in Liaoning-Jilin tectonic belt, on the basis of metallogenic geological conditions such as Paleoproterozoic structure-formation, to analyze previous data and research results and systematically discuss the sources of cobalt-nickel ore-forming material, characteristics of typical ore deposits or occurrences and mineralization process in Liaoning-Jilin tectonic belt. The results show that the Langzishan Formation to Gaojiayu Formation of former Liaohe Group is a complex orogenic accretionary series formed under the stable continental margin, active continental margin and even trench-arc-basin system. There is structural contact between the rock slices of different origin, showing the tectonic formation characteristics of overall disorder and locally order. The overlying Dashiqiao Formation-Gaixian Formation is stable residual sea basin sediment, which are in non-conformable contact with the underlying strata, showing the characteristics of ordered strata. Overall, the set of formation can neither be simply divided as ordered strata, nor be regionally correlated by metamorphic deformation degree. It is quite unreliable to judge the protolith formation of some metamorphic rocks and the tectonic environment in which they formed only by geochemical data and diagrams. The Liao-Ji granite(streaky or banded granite) formed by relatively mature continental margin arc, and the rock assemblage of the island arc generally displays the characteristics of TTG, but its ore-controlling significance is still unclear. The intrusive rocks formed under post-orogenic extension are predominantly syntectonic garnet granites or granitic gneisses which were deeply melted or remelted S-type granite. Additionally, there are adakitic granitic diorites that emerged in the context of late orogenic thickening. The ore-forming materials of the Cu, Co and Ni deposits are primarily sourced from basic dykes, continental crust pyroclastic rocks, subduction accretion complexes and abyssal sedimentary rocks. In the process of subduction and extinction for the Liao-Ji Ocean, besides the re-enrichment of original mineral source layer by orogeny and metamorphism, and the mineralization of basic-ultrabasic rocks under extensional action, the high carbonaceous quality and salinity in pelagic environment(seafloor thermal brines) are essential factors for mineral enrichment. In conjunction with regional geochemistry, three cobalt-nickel mineralization zones and six target areas are delineated within the Liaoning-Jilin tectonic belt. With an evaluation for the mineralization potential, the prospecting indicators and directions for cobalt-nickel deposits in the belt are proposed, which offer a novel approach to the prospecting breakthrough strategic action in the region.