Metallogeny and Exploration Implications of Carbonate- and Clastic-Hosted Zn-Pb Deposits in the Southwestern Tianshan, NW China

Lead (Pb) and zinc (Zn) are critical base metals whose sedimentary basin-hosted mineral systems form major exploration targets worldwide. Mississippi Valley-type (MVT) deposits represent one of the most important subtypes of sediment-hosted Zn-Pb mineralization and are concentrated within the Tethyan orogenic domain, where ore formation is commonly associated with fold–thrust belts and foreland basins developed along continental collision zones. The Southwestern Tianshan belongs to the southern Central Asian Orogenic Belt (Altaids). Although it is not part of the Tethyan domain, it experienced significant late-stage overprinting driven by far-field Tethyan tectonism that modulated regional ore formation. It hosts two types of sedimentary basins: Late Paleozoic remnant marine basins and Meso-Cenozoic foreland–intermontane basins. These contain Zn-Pb deposits hosted respectively in carbonate rocks (e.g., Hoxbulak) and clastic rocks (e.g., Uragen). This paper systematically reviews the geological and geochemical characteristics of these two deposit types, with emphasis on comparing their metal sources, ore-fluid properties, and mineralization ages. Carbonate-hosted Zn–Pb deposits include a Late Paleozoic sub-type (~258–260 Ma) and a Paleogene main stage (~55–45 Ma), whereas the clastic-hosted Uragen deposit formed mainly in the Paleogene (~55–45 Ma). The Paleogene event is broadly coeval with the India–Asia collision, while the Late Paleozoic sub-type may be related to the closure of the Paleo-Asian Ocean. Both are epigenetic MVT-type systems, but they represent distinct tectonic episodes. Mineralization represents a response to large-scale basinal fluid mobilization during continental collision. However, the two types differ systematically in metal sources: carbonate-hosted deposits derive Pb, Zn, and S mainly from the host carbonate strata themselves (stratabound), whereas the clastic-hosted deposit derives metals mainly from crustal materials supplied by orogenic denudation. Ore fluids in both types are dominated by basinal brines with participation of oil–gas fluids, but carbonate-hosted systems have moderate salinities (2.90–21.82 wt% NaCl eq.) with carbon from host carbonates, whereas clastic-hosted systems have higher salinities (7.22–20.29 wt% NaCl eq.) with carbon from organic matter. Carbonate-hosted deposits are primarily controlled by thrust fault systems and karst breccias, whereas the clastic-hosted deposit is controlled by synclinal structures and “source–reservoir–cap” assemblages. A four-element conceptual framework (tectonic activation, fault conduits, ore-hosting construction, and oil–gas reduction) is developed to organize the regional evidence and to generate testable exploration criteria. This framework is not presented as a validated predictive model, but as a working synthesis that links far-field collisional tectonics, basinal fluid flow, favorable host-rock traps, and hydrocarbon-driven sulfate reduction to Zn–Pb mineralization. Integrated exploration criteria are established, and favorable areas are delineated for future exploration in the Meso-Cenozoic foreland basins on the northwestern Tarim margin and the carbonate-dominated tracts in the South Tianshan margin and Kalpin uplift. The Southwestern Tianshan provides a key case for understanding the spatiotemporal coupling between continental collision and MVT mineralization in the Tethyan domain, with implications for exploration of similar deposits globally.