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In this paper, two kinds of knowledge-driven methods, one using the fuzzy logic and another using geometric average, were applied to create the mineral potential maps for Cu sulfide deposits in the greenfield Kapsan Basin, DPR Korea. The ore geology studies for the study area have revealed that Cu sulfide deposits of hydrothermal genesis in Kapsan Basin are closely associated with Jurassic intrusions and faulting tectonics. Based on the conceptual model of Cu sulfide deposits and the available spatial datasets in the study area, we used five independent evidential maps for Cu sulfide deposits potential mapping. They include: (1) faults; (2) aeromagnetic anomaly; (3) Cu geochemical data; (4) Pb geochemical data; and (5) Zn geochemical data. The evidential map values were transformed into continuous values of the [0, 1] range using the non-linear fuzzy membership functions; logistic sigmoid and fuzzy Gaussian functions. Because the fuzzy logic and geometric average methods can use the same fuzzification methodology based on suitable membership functions, it is very economic and efficient to simultaneously apply two predictive models for mineral potential mapping of the study area. The preparation of these evidential layers were performed using spatial analyses supported in ArcGIS 10.4 GIS platform based on geological, geophysical and geochemical spatial datasets. The validation and comparative analysis results for the two predictive models demonstrated that most of known mineral occurrences are distributed in areas with high potential values. The target areas classified by the fuzzy logic occupy 15% of the study area and contain 78% of the total number of known mineral occurrences. Compared with the fuzzy logic, the resulting areas by the geometric average occupy 13% of the study area, but contain 93% of the total number of known mineral occurrences. Although the total number of known mineral occurrences is relatively low for the application of ROC (receiver operating characteristics) technique, the areas under the ROC curve (AUC) obtained by two predictive models were greater than 0.5, suggesting that both predictive models and their resulting potential maps are useful for evaluating the prospectivity of Cu sulfide deposits in Kapsan Basin.

The Songhung deposit is located in the southwestern part of the Yangdok metamorphic core complex (YMCC) in the northern portion of the Pyongnam Basin, the eastern part of the Sino-Korean Craton. In this paper, we present a detailed study on the magma sources of the granitoids (Yangdok and Hoechang graintic intrusions), genesis of pyrite and fluid inclusion characteristics for sufficient and additional understanding of tectonic events, petrogenesis of the granitoids and mineralization in the study deposit. The Yangdok granite has lower Al2O3/TiO2 ratios (mean value of 60.58) than the Hoechang granite (mean value of 994.46), indicating the higher temperature magma source of the former. On the Rb/Ba vs. Rb/Sr and CaO/(TFeO + MgO + TiO2) vs. (CaO + TFeO + MgO + TiO2) discriminant diagrams, the magma source of the Yangdok granite belongs in the plagioclase-rich and clay-poor source rocks, while those of the Hoechang granite plots either in the plagioclase-rich and clay-poor source rocks (for granite and fine-grained granite) or in the plagioclase-poor and clay-rich source rocks (for granite porphyry and felsite). On the Nb vs. Y, Ta vs. Yb, Rb vs. Y + Nb and Rb vs. Yb + Ta tectonomagmatic discrimination diagrams, these two granites are connected with the volcanic arc-related setting and plot in post-collision setting. Moreover, some data of the Hoechang granite fall in WPG field, suggesting that the volcanic arc setting may be changed to an intraplate setting from Middle Cretaceous. The pyrite trace element geochemistry, showing the high Co/Ni ratio than one with an average of 8.2 and high Co content and low Ni content, suggests that its formation was closely linked with I-type granitic magma-derived hydrothermal fluid mixed with meteoric water. It could also be assumed by the Co and As contents in pyrite, indicating a certain degree of meteoric water in the ore forming fluid. It is consonant to the Pb, S, C and O isotope geochemistry in the previous study, suggesting that ore-forming fluids and metals could be derived from both the Yangdok granite and the Proterozoic and Paleozoic meta-sedimentary rocks exposed in the study area. All of the pyrite grains have not compositional zoning and the similar distribution patterns of Co and Ni are appeared in single pyrite grain (from core to rim), suggesting the stable crystallization environment of pyrites and same ore forming fluid source. In pyrite grains, the positive correlation between gold and arsenic is appeared. The Au exists either as a micro- and nano-size inclusion in pyrite and other minerals or as a solid solution in pyrite lattice. Based on the petrological and microthermometric characteristics of the fluid inclusions in ore-bearing quartz, we suggest that the ore-forming fluid is represented as NaCl + H2O or NaCl + KCl + H2O systems with low salinity. The absence of CO2-enriched phase and vapor-only or liquid-only primary inclusions in quartz indicates the homogenous magma-derived ore forming fluids and a lack of boiling during ore-forming process. The formation temperature and pressure of this deposit approximately vary from 317 to 326 °C and from 105.46 to 111.69 × 105 Pa, respectively, exhibiting the hydrothermal deposit origin. In conclusion, the Songhung deposit is originated from I-type granitic magma source-derived hydrothermal fluid which was mixed with meteoric water.

The Songhung deposit is located in the southwestern part of the Yangdok Uplift Zone (YUZ) in the northern part of the Pyongnam Basin in the Sino–Korean Craton. Most of large– and small–scale gold deposits and occurrences were discovered and exploited in the western part of the YUZ. Several tectonic events in this area are the key to understanding the gold and polymetallic mineralization in the Sonhung deposit. The YUZ comprises the Neoarchean Rangnim Metamorphic Belt, Proterozoic and Early Paleozoic rocks in the central domain, and granitoid intrusions of crustal and mantle derivation (Yangdok granitoid intrusions). Two extensive NNE–trending fault zones with mylonitized rocks are interpreted to represent detachment fault and two NE–SW–trending regional rift structures represent zones of subsidence (e.g., the Tokchon–Maengsan to the west, the Kowon to the east) and the Junghwa–Samdung subsidence to the south. It is suggested that the YUZ is a metamorphic core complex (MCC), similar to those in the North China Craton (NCC). Polymetallic mineralization in the Songhung deposit is divided into early and late stages. The early mineralization was formed during compressional deformation in the Triassic accompanied by low–grade metamorphism of the sedimentary host rocks. Variations in Pb, S, C and O isotope ratios indicate that the ore–forming fluids and metals were derived from the country rocks. The Au grade is insignificant in this style of mineralization. The main gold–polymetallic mineralization in the Songhung deposit is related to tectonic extension of the region; the Pb, S, C and O isotope data indicate that these elements, as well as ore–forming fluids, could be derived from both the granitic intrusion (Yangdok granitoid) and the Proterozoic and Paleozoic country rocks.