Magmatic Ni-Cu sulfide deposits formed by injecting of sulfide-bearing magmas segregated at depthare hosted in intrusions with high proportions of sulfide ores. The lithologic variations and distribution of sulfide orebodies in the intrusions are inconsistent with model of in-situ magmatic fractionation and sulfide segregation. Many such deposits had been identified in China. However, corresponding method for further exploration of the ore bodies in depth in these deposits has not been developed well. In this paper, we summarized marked geological features of this type of deposits in China, including the Jinchuan deposit. Exploration of the Voisey's Bay super-large Cu-Co-Ni sulfide deposit in Canada, which is genetically similar to the Jinchuan deposit, was described. We proposed that it is potential to prospect new ore-bodies along sulfide-bearing magma conduit at depth. We also presented method prospecting new ore bodies along the conduit of sulfide-bearing magmas in the Jinchuan deposit.
It is widely accepted that the incorporation of external sulfur via crustal contamination is an important trigger for sulfide immiscibility that generates Ni-Cu-(PGE) sulfide mineralization, yet other controlling factors for sulfide immiscibility may also be present. The late Permian Panzhihua, Baima, Hongge, Xinjie and Taihe layered intrusions in the Emeishan Large Igneous Province (ELIP, SW China), are well-endowed with Fe-Ti oxide deposits, whereas their sulfide mineralization is mainly sub-economic. For example, the lower part of the Xinjie intrusion hosts a few thin PGE-rich ore layers, yet other ELIP layered intrusions do not contain any Ni-Cu sulfide mineralization and are PGE-depleted (0.01--1 ppb). Compared with the PGE-undepleted Emeishan high-Ti basalts that are genetically related to the intrusions, the extent of PGE depletion and elevated Cu/Pd ratios (up to 3.2×10^6^) of the Panzhihua, Baima, Taihe and Hongge intrusions suggest PGE-depletion in their parental magmas due to early-stage sulfide removal. Sr-Nd isotopic compositions of the Panzhihua, Baima and Taihe intrusions suggest crustal contamination was insignificant and sulfide saturation produced mainly by crustal sulfur input was unlikely. MELTS modeling shows that extensive fractionation of chromite, olivine and clinopyroxene in deep-seated magma chambers may have induced early-stage sulfide saturation of the primary magmas. The relatively high sulfide contents in the Fe-Ti oxide layers at Panzhihua, Baima, Hongge and Taihe indicate a close relationship between the second-stage sulfide immiscibility and extensive Fe-Ti oxide crystallization. Positive correlations between sulfur and total Fe~2~O~3,~ V and TiO~2~ suggest that Fe-Ti oxide (magnetite and ilmenite) crystallization may have triggered the second-stage sulfide saturation via sharply lowering the Fe concentration and oxygen fugacity of the magmas. Moderate degree of crustal contamination for the Xinjie Fe-Ti oxide-barren rocks may have induced sulfide saturation and accumulation at the lower part of the intrusion. Our calculations indicate that the Xinjie PGE-rich rocks have high R-factors (1000--10000), which are ascribed to PGE-upgrading of the sulfides via reaction with new replenishments of PGE-undepleted magmas. A few Panzhihua, Baima and Taihe samples that contain higher PGE concentrations suggest that the early-stage sulfide droplets at depths were entrained in later magma pulses delivered to shallower magma chambers. The very high R-factors determined by mass balance calculation, implies a good potential for discovering more PGE mineralization in the deep-seated intrusions of the magma plumbing system.
Textural and compositional zoning within plagioclase phenocrysts record the magma chamber processes, such as magma differentiation, magma recharge and mixing, and crustal contamination. The plagioclase phenocrysts in the Daqiao and Qiaojia plagioclase-phyric basalts from the Emeishan Large Igneous Province (LIP) show complex textural and compositional zoning patterns, e.g., normal, reverse, oscillatory, and patchy zoning patterns. Most plagioclase phenocrysts exhibit a core–rim normal zoning pattern (Pl–A) with euhedral high–An cores (An=76–78 %, in mole fraction) and low–An rims (An=68–72 %), indicative of the crystal regrowth processes caused by recharge of relatively evolved magmas after the formation of high–An cores. Some phenocrysts have a core–rim reverse zoning pattern (Pl–B) with irregular ovaloid cores, characterized by extremely low An (60–61 mol%) and Ba (84–88 ppm) contents and extremely high 87 Sr/ 86 Sr ratios (0.7120–0.7130). The rims of the Pl–B have relatively high An (69~72 %), Ba (~160 ppm) contents and low 87 Sr/ 86 Sr i (~0.7056). These Pl–B plagioclase phenocrysts preserve the information about interaction between the crustal xenocrysts and the transporting magmas. Some plagioclase phenocrysts show a core–mantle–rim oscillatory zoning pattern (Pl–C) with multiple oscillations of An (70–80%), Ba (88–147ppm) from core to rim, revealing replenishment and mixing of multiple batches of basaltic melts with diverse compositions. 87 Sr/ 86 Sr ratios of the PL–C do not vary significantly (0.7050–0.7054). A small portion of phenocrysts have patchy patterns in the cores (Pl–D), where the low–An patches (72–75 %) in form of elliptical or irregular elongated shapes were enclosed by the high–An domains (80–87 %). These features can be attributed to crystal dissolution and regrowth processes during reaction between early-formed low–An cumulates and recharged hot primitive melts. The cores, mantles, and rims of different types of plagioclase phenocrysts (with the exception of Pl–B) commonly display nearly constant Sr isotopic compositions, implying insignificant wall-rock assimilation at shallow-level magma resevior(s) during growth of these plagioclase phenocrysts. Extensive crystallization of plagioclase has played an important role in the formation of iron-rich basalts in the Emeishan LIP.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='rotate(144 450 300)'/%3e%3cuse xlink:href='%23a' transform='rotate(216 450 300)'/%3e%3cuse xlink:href='%23a' transform='rotate(288 450 300)'/%3e%3c/svg%3e)