| After the continent to continent collision of the Yangtze and North China Craton in the late Triassic, the basic near EW-NW tectonic lines in east Qinling orogen are formed in the following intracontinental orogeny. Crustal rotations at the late Mesozoic triggered the N(N)E trending faults, and formed a network structure based on the NWW framework and secondary N(N)E fabrics. The Mo bearing granitic magma intruded in the conjunction of the faults, forming the numerous Acid-intermediate porphyritic granites, skarn and porphyry metallogenic system. The statistics of the tectono fissures attitudes, shows that they are mainly occurring in the N(W)W trending, in accordance with that of strata. In some parts, the fissures closely related to the hydrothermal activity are distributed in the N(N)E trending tensional veins. At-157Ma, the tectonic regime was in transition from a syn-collisional to a post-collisional setting, still in the N-S trending convergent tectonic.-115Ma, the tectonic regime changed into within plate, from compression to extension;-146Ma, ore-bearing plutons, which are triggered by slab melts, formed at the junctions of NWW-NE faults.Luanchuan ore belt is located in the key metallogenic area in the east Qinling orogen. Acid-intermediate granites in the north of Luanchuan area (abbr:ore-bearing plutons) are of the characteristics of "small plutons bearing large ore deposits" and are close to the intense Mo-polymetallic mineralization at late Mesozoic; The Laojunshan rock is distributed as batholith in the south, and sparsely Mo mineralization or Mo occurrences are existed. Both the ore-bearing rocks and the Laojunshan rocks are highly siliceous and shoshonitic, high-K calc-alkaline, similar to some I-type granites. Both rock suites are enriched in Light rare earth elements (LREEs) and of negative Eu anomalies.(La/Yb)N ratios, Eu values,(La/Sm)N values in the ore-bearing granitoids have higher concentrations than that of the barren Laojunshan granite suite, confirming the observation that the ore-bearing granites have undergone a higher degree of strong differentiation than that of Lanjunshan batholith. The Laojunshan rocks undergone greater fractionation of heavy rare earth elements (HREEs), indicating more crustal materials were contaminated in the granitic evolution process. Comprehensive isotopic study suggests that the metallogenic and lithogenetic materials are mainly from lower crust, involvement with parts of mantle composition.Ore-bearing rocks are complex plutons, including granodiorite, monzonitic granite and porphyries (or aplites) from early to late. The isotopic ages of monzonitic granites from deep boreholes are153.2±1.3Ma,154.1±1.8Ma, respectively. Zircon isotopic age of aplite from ore adit is148.3±1.0Ma, suggesting that the evolution of Mo-bearing granitic magma is long, Re-Os data are concentrated in-146Ma.The place where tectono-geochemistry method shows that ore-forming elements, such as Mo-W-Pb-Zn-Ag are of evident anomalies which are coincide with the La-Rb-Sr-K2O anomalies have the higher potential of mineralization in the deep; in the stage of detailed mineral exploration, comprehensive application of CSAMT and SIP is a effective method for ore body positioning.A new model called continuum model that ore-bearing granites experienced sequential chamber evolutions is proposed to explain the Mo enrichment processes. It is through the sequential granitic chambers that Mo was gradually enriched. Finally, huge Mo reserves were accumulated in the Luanchuan ore belt. The model might be a paradigm in explaining the pervasive Mo genesis in late Mesozoic of the east China. |
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