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The article discusses the research study conducted to examine the geologic history of the iron oxide copper gold (IOCG) deposits in Southwestern China that was associated with polymetallic mineralization. It reveals the age of magmatic rocks and metallogenic epoch and the coupling relationship between polymetallic elements. It also reveals the ore-forming process including the volcanic sedimentation, grenville orogenic event, and superimposed mineralization.

Accurately constraining the age and source of primary U mineralization is commonly difficult as diverse U minerals are affected by α-recoils and subjected to overprints of multi-stage fluids. Titanite has a good potential in revealing rock-forming and metallogenic information, and widely occurs in magmatic, metamorphic, and hydrothermal U deposits. However, the textural and chemical characteristics of titanite from these U deposits are poorly documented and little is known about the relationship between titanite and U mineralization. At the western margin of the Yangtze Block, a series of U occurrences and uraninite-predominant ores are hosted in the leucocratic dykes, ranging from fine-grained (albitised) monzogranite to pegmatitic quartz vein. The genesis of U mineralization remains unclear largely because of the uncertainties as to the timing of mineralization and the origin of metals. Here, we present comprehensive U Pb and Sm Nd isotopic data, and major and trace element compositions for metamorphic (Ttn-I) and magmatic/hydrothermal (Ttn-II) titanites from the leucocratic dykes and/or amphibolitic wall rocks. Ttn-I is in direct contact with metamorphic hornblende and plagioclase or occurs as xenoliths hosted in the leucocratic dykes, and is thus inferred to result from amphibolite facies metamorphism. Chemically, Ttn-I is characterized by low Fe/Al ratios, LREE-depleted patterns and weakly negative to positive Eu anomalies. By contrast, magmatic/hydrothermal Ttn-II crystals intergrown with uraninite in the leucocratic dykes generally display flatter REE patterns, more negative Eu anomalies, higher Fe/Al ratios, and U, Nb, REE and Y contents, which could be applied as an indicator for U exploration. LA-ICP-MS U Pb dating on Ttn-I yielded ages of ∼860 Ma for amphibolite facies metamorphism. Instead, U Pb dating on syn -ore Ttn-II yielded ages of ∼786–779 Ma for U mineralization, which is coeval with the emplacement of leucocratic dykes. Uraninite and intergrown Ttn-II have uniform, negative εNd(t) values (−5.7 to −15.5), indicating the initial melts were predominantly sourced from the old crustal materials (T DM2 = ∼1.9–2.7 Ga). Considering the occurrences as dykes, feldspar-quartz-dominant lithologies, and wide textural and compositional variations of leucocratic dykes, we infer that low-degree partial melting of U-rich protolith is the main factor controlling U concentration in the melt. Variable REE patterns and ThO 2 contents in different uraninite types seem to imply there have been multi-stage U mineralization. • Dyke-hosted U mineralization at the western margin of the Yangtze Block formed at ∼786–779 Ma. • The uraniferous leucogranitic magma was derived from old crust with a T DM2 of ∼1.9–2.7 Ga. • Low-degree partial melting process may be the main factor controlling U concentration. • Titanite with high REE, Y, Nb, and U contents could be applied as an indicator for U exploration. [ABSTRACT FROM AUTHOR]

• Pyrite hosting visible gold is low in Au and As. • Gold-bearing pyrite was subject to brittle rather than ductile deformation. • Visible gold in pyrite did not result from remobilization of lattice gold. • Visible gold in pyrite was introduced by evolved ore fluids after host pyrite. Pyrite (FeS 2) is one of the most common hosts for gold (Au) in different types of gold deposits, including visible and invisible gold. For visible gold in pyrite, it remains unclear whether it resulted from remobilization of invisible gold in the gold-hosting pyrite or from external input. This paper reports a case study from the Zhaoxian gold deposit, which is the deep extension of the well-known Jiaojia gold deposit, in the Jiaodong gold province. The texture and composition of Au-bearing pyrite from the Zhaoxian deposit were studied with petrographic, Electron Back-Scattered Diffraction (EBSD) mapping, and Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) methods. Four types of pyrite (Py-1 to Py-4), corresponding to four generations of veins, i.e., the pre-ore V1, syn -ore V2 and V3, and post-ore V4, were distinguished. Py-2 is volumetrically the most abundant among the four, and is the main host of visible gold. LA-ICP-MS analyses of pyrite indicate that gold contents in most analysis points are below the detection limit, with measured Au contents ranging from 0.02 to 0.17 ppm (median 0.09 ppm) in Py-1, and 0.03 to 2.45 ppm (median 0.07 ppm) in Py-2. EBSD analyses indicate that pyrite (Py-2) display brittle deformation features including microstructures, lattice dislocation, and grain boundary displacement. Visible gold in Py-2 occurs in micro-fractures, cavities, and grain boundaries. The generally low contents of Au in pyrite, including Py-2, and the brittle deformation features, suggest that the visible gold grains did not result from remobilization of invisible gold from pyrite. Rather, the majority of gold was introduced by fluids after the formation of the gold-hosting pyrite. These fluids were derived from the same sources as those precipitating the gold-hosting pyrite, but were more evolved and enriched in Au. Circulation of these auriferous ore-forming fluids in microfractures of pyrite and interstitial space resulted in precipitation of visible gold. [ABSTRACT FROM AUTHOR]