A Novel Approach to Three-Dimensional Inference and Modeling of Magma Conduits with Exploration Data: A Case Study from the Jinchuan Ni-Cu Sulfide Deposit, NW China

The genesis of magmatic Ni-Cu-precious metal sulfide ore deposits in open system magma conduits provides a means to reconcile the very large ratios of sulfide to magma in relatively small mafic-ultramafic intrusions. The Jinchuan Intrusion in Gansu Province, NW China, is a classic example where the relationships between the chonoliths and ores can be investigated with extensive exploration data on Ni and Cu concentrations generated during exploration, development, and mining. Along these lines, in this work, a novel approach for inference and modeling of magma conduits with exploration data is proposed. More specifically, for the reconstruction of three-dimensional models (3D) of magma conduits, a Markov random field (MRF) model, which is solved by utilizing a graph cut algorithm (an algorithm for n -dimensional image segmentation), was developed to find a globally optimal solution, in terms of segmentation of the pattern of magma conduits from the exploration data. In addition, a specialized implicit 3D modeling scheme was devised to generate automatically the underlying 3D geometry of the magma conduits from the solutions of the MRF. The proposed approach was used to establish the 3D architecture of the magma conduit system at Jinchuan, and it illustrated the presence of three different magma conduits. The western intrusion resulted from a bifurcated magma conduit whose entrance was located at the bottom of segment III and its major branch extended sub-horizontally to the southeast of the intrusion. The formation of the eastern intrusion was attributed to two "funnel-shaped"magma conduits whose entrances were located at the bottom of Nos. 1 and 2 orebodies, respectively. The reconstructed magma conduits were supported by evidence from lithological assemblages, grained sizes of olivine, ore-style distributions, and spatial variations of PGE tenors, which reflected the effectiveness and robustness of the proposed approach in 3D inferring and modeling magma conduits. Following the dip direction of the associated magma conduits, the refined locations structurally below orebodies 1, 2, and III-1 were expected to have a high potential for mineral exploration.