Stratiform Exhalative-Volcanogenic Tungsten (Cu-Zn) Mineralization in Chah-Calap Deposit and its Ore-Bearing Horizons

Chah-Calap W (Cu-Zn) deposit is located in Lut Block. It is a part of Central Iran Paleozoic platform which has been subjected to late Cimmerian orogenic movements. Chah-Calap ore- bearing volcano-sedimentary sequence of upper Triassic-Jurassic age was metamorphosed to green schist-lower amphibolite facies. This sequence includes siliceous meta-pellite, lower meta-felsic tuff, meta-limestone with meta-chert interlayers, (main mineralized horizon occurred at the base of it) alternation of micritic and sparitic limestone, upper meta-felsic tuff and mylonitic rhyolite. In meta-limestone, 3 facies were recognized, in which the mineralization corresponds only to meta-chert bearing facies. No intrusive body outcrops in the study area. Two NW-SE and NE-SW trending fault systems can be observed in Chah-Calap mining region. The stratiform mineralization with layering and lenticular geometry has 2 kilometer length. Based on these investigations, six mineralized horizons can be distinguished in Chah-Calap volcano-sedimentary rocks: siliceous meta-pellite (ore horizon I), lower meta-felsic tuff (ore horizon II), calc-silicate layers, bands and lenses occurring at the contact between meta-limestone and lower meta-felsic tuff (ore horizon III), at the middle of meta-limestone layer (ore horizon IV) and at the upper contact between meta-limestone and upper meta-felsic tuff (ore horizon V) and mylonitic rhyolite host rocks (ore horizon VI). Main mineralized horizon in Chah-Calap occurred at the base of meta-cherty limestone, at lower contact between meta-carbonate and lower meta-felsic tuff. Regionally metamorphosed chert-bearing parts of meta-limestone, forming calc-silicate horizon, composed mainly of sparitic calcite, tremolite, actinolite, diopside, hedenbergite and grassular-rich garnet. Ore assemblage includes: scheelite, chalcopyrite, sphalerite, pyrite, arsenopyrite, pyrrhotite, covelite, bornite, chalcocite, azurite/malachite and iron-oxide/hydroxides having massive, disseminated, laminated, breccia like and open space filling textures. Tungsten mineralization in Chah-Calap is considered to be of distal syn-sedimentary-syn-diagenetic type with exhalative origin. Diagenetic processes lead to primary concentration of mineralization which later experienced remobilization and re-concentration during regional metamorphism.