Writers : Ali Reza Monazami Miralipour; Supervisor: Dr. Ebrahim Rastad; Advisor: Dr. Mosaieb Sabzehei
Refference : Msc. Thesis
Publishing Year : 1998

Abstract :

Sheikh-Ali abandoned copper mine is located at 150 km south-east of Baft and 26 km south-east of Dowlatabad. The deposit occurs in south-east part of Zagros ophiolite melange zone. Several old mines and ore indications such as Ahmadabad and Baghchenar can be found in these ophiolite melanges.
Geological units essentially consist of spilitic lavas with pillow structure, diabases,?? pelagic limestones, radiolarian banded cherts and calcareous sandstones. The assembelge is separated by fault from serpentinite and ultramafic rocks. Ultramafic rocks include dunites, harzburgites and chromite-bearing serpentinites. Basaltic lavas and diabases are identified as ocean floor tholeiite to calc-alkaline series. The rocks have experienced chloritic, sericitic, propylitic and carbonate alteration. Pelagic limestones include pink to creamy micritic thin bedded limestones?? which have Upper-Cretaceous Maestrichtian microfossils.
General trend of pelagic limestones is east-west with high and variable dips; sitting along basaltic lavas. The contact between pillow lavas and pelagic S limestones is normal and variations in thickness and lateral facies are very common in these units. Radiolarian banded cherts with variable thickness,% between 10 cm and 10 m, and same strike and dip as pelagic limestones occur in > contact or near the contact between basalts and pelagic limestones. The horizon is country rock to ore mineral which in some places is brecciated and associated. with carbonate veinlets. Extension of the horizon is about 700 meters with an east-west trend (general strike of pelagic limestones). Old mining is seen as a trench with 120 meters length, 30 meters width and 30 meters present depth; several bore holes and huge bulk of slags. In Ahmadabad old mine and Baghchenar ore indication the ore horizons?? occur in contact between radiolarites and basaltic pillow lavas as sulfide rich lenses, which are strongly oxidized, with variable thicknesses (up to 5 m).
Ore geometry is essentially layered and also as massive lenses of 40 to 70 cm thick. In hand specimen and microscopic scales, ore textures are laminated, massive and disseminated. Laminated and massive ores are mostly associated with gel-shaped cryptocrystalline silica and disseminated ore is observed along with crystalline cherts.
Ore paragenesis is simple and consists of pyrite, chalcopyrite, sphalerite covellite, bornite, native copper and iron oxides. Pyrite is observed in three forms, euhedral, subhedral and colloform (pyrite-melnicovite).
Mean of Cu in massive ores is 2.5 percent, while in basaltic rocks is fourfold of that of standard tolleiitic basalts. Zinc and cobalt variations in ore zone art! congruent with Cu variations. The Au maximum content in massive ore is 0.64 g/t. Correlation coefficient of Cu and Zn is very high in basalts and ore sampled On the basis of following reasons, Sheikh-Ali copper deposit could be regard©, as a Cyprus-type volcanogenic massive sulfide deposit:
-Ore country rock is a part of volcanic and sedimentary units of Cretaceous. ophiolitic melange, which has the same strike as pelagic limestones and pillow lavas.
-Ore geometry is mainly lenticular conformable to the layering in pillow lavas and pelagic limestones.
-Paragenesis of ore elements, which are Cu, Zn, Fe and also presence of geochemical correlation between Cu and Zn.
-Presence of chloritic, sericitic, propylitic and carbonate alterations in basalt: rocks.
-Absence of plutonism and related processes to source of Cu in the area.
-Considering the extension of these melange zones towards out of Iran north-west to Turkish ophiolite melanges and their Cyprus-type massive sulfide deposits (for example: Ergany, Kur, ...), and in south to Oman ophiolites an their Cyprus-type massive sulfide deposits (for example: Lasail, Bayada, ...), an also through attention to recognition of this type deposits in other ophiolite zones in Iran, such as Ghezeldash deposit in Khoy ophiolite melanges,? : north-west Iran and Remeshk deposit in south Jaz-e-Murian this deposit can be attributed to Cyprus-type volcanogenic massive sulfide deposits.
Ore mineral is formed at late stages of submarine volcanic exhalation contemporaneous with deposition and diagenesis of gel-form siliceous sediment and banded cherts. The source of silica is mainly volcanic fumaroles an exhalates with a minor contribution from organic silica sediments and radiolarian shells. Also, the source of Cu and other metal ions is H2S rio volcanic fumaroles and exhalates.

Subject List : copper, Ophilite