Geology and chronology of the Zhaofayong carbonate-hosted Pb–Zn ore cluster: Implication for regional Pb–Zn metallogenesis in the Sanjiang belt, Tibet

• Sm–Nd isochron ages of calcite in MVT Pb–Zn ores forming in thrust belts were got.
• Pb–Zn mineralization happened resulted from thrusting and the post-thrust extension.
• The Pb–Zn ages indicate the India–Eurasia collision was from Southeast to Northwest.

Mississippi Valley type (MVT) Pb–Zn deposits can occur in orogenic thrust belts. However, the relationship between MVT ore-forming processes and thrusting is unclear. The 1500-km-long Sanjiang Metallogenic Belt in Tibetan Plateau is an important thrust-controlled MVT ore province with 860 Mt at 0.76–2.3% Pb, 0.3–6.1% Zn. The Zhaofayong MVT ore cluster in the Changdu area is a typical sample. The orebodies in this ore cluster are hosted in limestone, controlled by secondary faults to regional thrusts and forming along these faults. Two Pb–Zn mineralization stages in this cluster are recognized. Stage I is characterized by coarse and euhedral galena + sphalerite + calcite + fluorite + barite and Stage II by fine grained sphalerite + galena + pyrite + calcite. Sm–Nd isotopic dating of calcite forming in Stage I yields isochron ages of 41.1–38.1 Ma, suggesting the mineralization formed during extension following the first regional compression in the Changdu area. The connection between Stage I mineralization and the regional thrusting in the Changdu area can extend to the whole Sanjiang belt. Two stages of regional Pb–Zn mineralization are recognized between 65 Ma and 30 Ma and between 30 Ma and 16 Ma in the belt. The two Pb–Zn mineralization stages are consistent with those regional episodic thrusting activities and both of them immediately occurred after the episodic thrusting. An interpretation of the regional Pb–Zn mineralization is that regional compression forced the movement of hydrothermal fluids along regional thrust-nappe detachment faults and subsequent post-thrust extension caused the migration of hydrothermal fluids to the ore forming locations. The two mineralization stages in the Sanjiang Belt indicate complex processes related to India–Eurasia collision and the gradually younger mineralization ages from southeast to northwest indicate the collision follows the same direction.

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