The Jiangnan orogen, one of the largest gold-producing areas in China, has experienced multiple orogenic events with complex structural overprinting that is marked by multiple stages of magmatism, deformation, metamorphism, and orogenic gold mineralization. Different orogenic events have been recognized in the Neoproterozoic, mid-Paleozoic, Triassic, and Early Cretaceous, reflecting collisions and intracontinental orogenic episodes. The age of gold deposition in the Jiangnan orogen, however, has been poorly constrained owing to the absence of suitable dating minerals. Field studies in the orogen indicate the Tuanshanbei gold deposit includes two generations of auriferous quartz-ankerite-pyrite-arsenopyrite veins (Q2 and Q3), with the latter of the two notable for containing more abundant ankerite and base metal sulfides. The Q2 veins were formed throughout the near S-N–directed shortening associated with D₁ deformation and along resulting subhorizontal to low-angle-dipping EW- to WNW-striking transpressive faults. The Q3 veins, containing about 70% of the total gold resource, were primarily localized in moderately to steeply dipping NW-striking tensional/tensional shear faults and moderately dipping NE- to NNE-striking transpressive faults that were products of NW-SE–directed shortening during D₂ deformation. Both vein generations are temporally younger than the 437.2 ± 4.2 Ma Tuanshanbei granodiorite host, and both are crosscut by postgold ca. 225 Ma diabase dikes. Hydrothermal monazite coexists with native gold and gold-bearing metal sulfides in the Q2 and Q3 veins. The Q2 monazite yielded a Tera-Wasserburg lower intercept age of 415.1 ± 2.1 Ma, consistent within error with an ankerite Sm-Nd isochron age of 410 ± 15 Ma and a laser ablation-inductively coupled plasma-mass spectrometry hydrothermal zircon ²⁰⁶Pb/²³⁸U age of 411.2 ± 4.0 Ma. The Q3 monazite yielded a Tera-Wasserburg lower intercept age of 234.3 ± 1.1 Ma. These new ages suggest that the Early Devonian gold event was overprinted by hydrothermal activity along the same structural system almost 200 m.y. later such that the gold resource must be a product of two temporally distinct events. Geologic and structural evidence, coupled with existing published geochemical data, suggests both ore-forming events were related to crustal metamorphism typical of most orogenic gold deposits. Fluids would have been derived from Neoproterozoic metasedimentary basement rocks, most likely from metamorphic devolatilization of the Neoproterozoic Cangxiyan Group greenschist-amphibolite facies metasediments. There is no evidence suggesting any type of magmatic contribution to the ore-forming process at either time. The data are best interpreted to suggest that various parts of the basement were metamorphosed near the greenschist-amphibolite boundary at different times, but during both times, the gold-bearing metamorphic fluids eventually migrated into the same structural conduits.

LCT (Li-Cs-Ta) rare-element pegmatites occur as late-stage and highly-fractionated bodies at the margins of regionally zoned granite pegmatite fields. The evolution of the granitic pegmatite system, including its rare-metal metallogeny is often difficult to determine due to complex textures involving variable crystal size, and a heterogeneous chemical composition. The Renli-Chuanziyuan pegmatite field (South China) displays a well-developed regional zonation sequence, involving a core of biotite-, two-mica-, and muscovite-monzogranites that grades outward into microcline (K-zone), microcline-albite (K-Na-zone), albite (Na-zone) and albite-spodumene (Na-Li-zone) pegmatites. Monazite and the Th, Ca-endmember (i.e., cheralite) provide valuable age, rare earth element (REE) geochemical, and Sm-Nd isotopic data for understanding the regional zoning process within the Renli-Chuanziyuan pegmatite. Monazite (from the muscovite monzogranite (MM), and the K-, K-Na-, and Na-zone pegmatites) and cheralite (from the Na-Li-zone pegmatite) have variable compositions and complex internal microtextures. The monazite and cheralite grains contain irregular areas with subtle heterogeneous BSE response along cracks and grain-margins, suggesting that they have experienced alkali-bearing fluid-aided modification. However, these features are rarely seen in monazite from the K-zone pegmatite. Common Pb contamination and/or Pb loss during fluid-aided modification may have disturbed the monazite and cheralite U-Th-Pb isotopic system, due to the differential mobility of U, Th and Pb. The unaltered Na-zone monazite and Na-Li-zone cheralite yielded Th-Pb ages of 140.42 ± 2.30 Ma (2 σ, MSWD = 2.4, n = 14) and 139.58 ± 2.15 Ma (2 σ, MSWD = 2.9, n = 21), respectively. The unaltered MM, K-zone and K-Na-zone monazite yielded ²⁰⁶Pb-²³⁸U ages of 138.03 ± 2.18 (2 σ, MSWD = 2.5, n = 18), 140.39 ± 2.18 (2 σ, MSWD = 3.0, n = 20) and 140.58 ± 2.14 Ma (2 σ, MSWD = 2.0, n = 52), respectively. These ages for the four pegmatite zones are temporally consistent with a syngenetic origin for the magmatic sequence of biotite-, two-mica-, and muscovite-monzogranite and the pegmatite system and rare metal (Li-Nb-Ta-Rb-(Cs)-(Be)) mineralization. The Sm-Nd isotopic analyses of the unaltered monazite and cheralite from the MM and four pegmatite zones yield similar initial Nd isotopic composition with εNd_(t) = -9.9 to -7.9, indicating an identical single source region (i.e., the Neoproterozoic South China lower crust). The Sm/Nd ratios display a gradual decrease across the four pegmatite zones from the unaltered K-zone monazite to Na-Li-zone cheralite, i.e., 0.39 – 0.63 (avg. = 0.43) for K-zone, 0.29 – 0.35 (avg. = 0.31) for K-Na-zone, 0.26 – 0.30 (avg. = 0.28) for Na-zone, and 0.21 – 0.27 (avg. = 0.24) for Na-Li-zone. Such progressive variations suggest their derivation from the same parental magma, which experienced varying degrees of fractionation prior to the extraction of pegmatitic melts. Comprehensive monazite and cheralite geochemistry, as well as in-situ U-Th-Pb and Sm-Nd isotopic results indicate that Rayleigh-type fractional crystallization controls the mineralogical and geochemical evolution from a chemically zoned granite source.