The gold mineralization system of the Jiaojia fault belt in Jiaodong

More than 60 gold deposits have been discovered within the Jiaojia fault belt, its footwall-derived subsidiary faults and fractures, and the interlayer-sliding zones formed by interference between basement folds in the hanging wall. These deposits contain proven gold resources exceeding 1, 700 tons, constituting four gold mineralization sub-systems: (1) The Jiaojia main belt gold mineralization sub-system, which includes orebody Group Ⅰ, Ⅱ and Ⅲ. (2) The Wang'ershan fault gold mineralization sub-system, and (3) the Lingbei fault gold mineralization sub-system, each comprising orebody Group Ⅰ, Ⅳ and Ⅴ. (4) The basement fold interference gold mineralization sub-system, whose known orebody groups occur within isolated structural basins. The first three sub-systems are controlled by a rhombic fault network developed in the footwall of the Jiaojia fault, whereas the fourth is located in its hanging wall. The Jiaojia main belt sub-system hosts 23 gold deposits with proven resources of 1, 385.15 tons. Among them, the orebody group Ⅰ, the major mineralization zone controlled by the main fault, is characterized by fine vein-disseminated gold mineralization of pyrite-sericite-quartz type; the orebody group Ⅱ, the secondary mineralization zone controlled by the main fault, subsidiary footwall faults, and dense joint systems. It contains both sericite-quartz-pyrite type and quartz vein type gold mineralization in the form of thin veins and stockworks; the orebody group Ⅲ, the smallest one, is controlled by steeply dipping subsidiary faults and sparse joints in the footwall, showing dominantly steeply dipping quartz-vein and stockwork-type gold mineralization. The Wang'ershan fault sub-system contains seven gold deposits with 132.41 tons of proven resources. The orebody group Ⅰ, hosted in the core of the Wang'ershan fault, represents the main orebody and is characterized by fine disseminated and massive gold mineralization. The orebody group Ⅳ, controlled by steeply dipping subsidiary faults and a series of left-stepping en echelon joints in the footwall, exhibits both pyrite-sericite-quartz and quartz-vein fine disseminated and vein-type mineralization. The orebody group Ⅴ, controlled by steeply dipping subsidiary faults and joints in the hanging wall, is dominated by quartz (±sulfide) vein and stockwork-type mineralization. The Lingbei fault sub-system includes 28 gold deposits with 191.7 tons of proven resources. Its characteristics are similar to those of the Wang'ershan fault sub-system, but individual deposits (or orebodies) are smaller in scale and dip in the opposite direction, forming a near mirror-symmetric relationship between the two. The basement fold interference sub-system hosts four gold deposits with 12.32 tons of proven resources. These deposits are controlled by interlayer-sliding zones formed during interference of regional Precambrian basement folds. Mineralization occurs within early nearly upright, groove-like tight folds trending NW (~300°) and later oblique broad folds trending NNE (~15°), filled respectively by milky quartz-coarse pyrite veins and smoky quartz-fine pyrite, quartz-polymetallic sulfide, or quartz-carbonate veins. Major ore-forming elements across all sub-systems include Au, Ag, Cu, Pb and Zn. Within the Wang'ershan fault sub-system, Au grades are generally similar among the orebodies, while Ag contents increase progressively from orebody Ⅰ to Ⅴ. The Cu, Ag and Pb contents of Jiaojia orebody Ⅱ and Wang'ershan orebody Ⅰ, as well as Jiaojia orebody Ⅲ and Wang'ershan orebody Ⅵ, are comparable. The δ34S values of pyrite from all four sub-systems show overall similarity and narrow variation, indicating a single sulfur source and the absence of significant external fluid mixing or compositional change during mineralization. The three subsystems in the rhombic lattice fault system all contain pyrite with similar Pb isotopic signatures, suggesting a common origin from the lower crust that was modified by mantle-derived materials.The geological and geochemical evidence collectively indicates that the Jiaojia fault belt gold metallogenic system resulted from long-term tectonic-fluid coupling, with sub-systems that are genetically related yet individually distinct: (1) the basement fold interference sub-system formed under a compressional tectonic regime, with gold mineralization occurring during crustal shortening. Sulfidation reactions and fluid immiscibility during early folding formed thick orebodies, while late-stage flashing of overpressured fluids within interlayer-sliding zones generated ore shoots; (2) the rhombic fault network sub-systems formed under a transcurrent tectonic regime, with gold mineralization occurring during the transition from ductile-brittle to brittle deformation and from compressional-shear to extensional-shear regimes. Intense early water-rock interaction and fluid phase separation produced the fine vein-disseminated and stockwork mineralization that established the overall framework of orebody groups Ⅰ and Ⅱ. Moderate late-stage water-rock reaction and pronounced fluid immiscibility controlled the formation of orebody groups Ⅲ, Ⅳ and Ⅴ (particularly quartz-vein orebodies) and superimposed nearly vertical high-grade ore columns upon the earlier orebodies Ⅰ and Ⅱ. Gold orebodies delineated so far are concentrated within a 10km section between Xincheng and Sizhuang along the Jiaojia fault, whereas the northern and southern segments remain poorly explored. Three-dimensional analysis of ore-controlling structures and quantitative modeling of orebody geometry reveal southward extension of these structures and mineralization enrichment patterns, defining 13 exploration targets. Preliminary drilling verification has intersected gold mineralization in 89 boreholes within the main belt subsystem and identified a new orebody (9.5m thick, grading 1.65~5.79g/t Au) in the Wang'ershan fault sub-system, confirming the validity and applicability of the metallogenic model and exploration predictions, and providing a clear direction for future prospecting.