Geological Characteristics And Metallogenic Regularities Of Porphyry Copper Deposits In Iran-Pakistan Belt

:The Iran-Pakistan porphyry copper belt is important part of the Tethyan metallogenic domain which extends from northwestern Iran to Western Pakistan.On the basis of the digestion and absorption of the past data and the advanced research results, by studying mineral chemistry, major and trace element geochemistry of the ore-bearing porphyry bodies, and analysing typical deposits and tectonic evolution of the Iran-Pakistan belt, author researches on the characters of spatiotemporal distribution, mineralization, alteration and ore-controlling factors. The metallogenic model of the Sahand-Bazman Miocene porphyry copper deposits in the collisional orogen have been proposed in the paper.The main achievements are made as follows:1. The ore-bearing of the Sahand-Bazman porphyry copper belt shows calc-alkaline and high-K calc-alkaline affinity. But the porphyry copper deposits in Chagai belt are associated with normal calc-alkaline rocks. But adakites are formed in different setting:the ore-hosting porphyries of the Sahand-Bazman porphyry copper belt be formed in collisional environment, the ore-bearing intrusions of Chagai belt related to subduction environment.2. Cl chondrite-normalized REE variation patterns of ore-hosting pophyries show overall steep REE profiles due to light REE-enriched and heavy REE-depleted signatures. Primitive mantle-normalized trace element variation diagrams of ore-hosting intrutions show enrichments in large ion lithophile elements(Rb, Th, Sr, Pb), and negative anomalies for high field-strength elements(Ta, Nb, Ti, Zr, Y, Ba).3. The different characteristics of trace element in the porphyry copper sub-belts indicates that the ore-hosting porphyries are derived from different magmatic sources. The ore-hosting porphyries of the Sahand-Bazman porphyry copper belt are likely derived from partial melting of thickened basaltic lower-crust, whereas the ore-hosting intrusions of the Chagai porphyry copper belt are likely related to partial melting of subducted oceanic slab.4. A classic concentric alteration pattern, approximating the overall geometry of Lowell and Guilbert (1970) model, is typically developed in the porphyry systems of the Iran-Pakistan belt:a central potassic alteration zone is surrounded progressively outward by sericite-clay-chlorite, sericitic, and propylitic assemblages. Mineralization is concentrated in potassic alteration zone, especially in the late stage of biotitic alteration.5. Metallogenic age of porphyry Cu deposits in the Iran-Pakistan porphyry Cu belt tends to younger gradually, from west to east and north to south, which is associated with tectonic evolution. Their spatial-temporal localization is controlled by strike-slip fault. The ore-bearing intrusions are emplaced in tensional pull-apart domains formed between two secondary strike-slip faults of the regional shear system. Porphyry copper deposits in the Iran-Pakistan belt occur predominantly at the inter-section of faults and the core of anticline.