Geology and economic potential for chromite in the Zhob Valley ultramafic rock complex, Hindubagh, Quetta division, West Pakistan

Abstract

The ultramafic rocks making up the Zhob Valley igneous complex have yielded small amounts of metallurgical-grade chromite since the early part of the century. From 1968-1970 a cooperative study undertaken by the Geological Survey of Pakistan and the U. S. Geological Survey, under the auspices of the Government of Pakistan and the Agency for International Development, evaluated the chromite potential of the Zhob Valley area and provided data for effective exploration. The Jung Tor Ghar ultramafic rock mass, covering an area of about 45 square miles, is a thrust-fault block completely surrounded and underlain (?) by sedimentary rocks as young as Late Cretaceous in age. The igneous rocks were thrust from the northwest along an east-trending, north-dipping fault in Late Cretaceous or Paleocene time and were peneplaned, dissected, and deeply laterized by mid-Eocene time. The ultramafic rocks consist of interlayered harzburgite and dunite and a cross-cutting dunite here called transgressive dunite. Layered structure passes without discernible deviation from the interlayered harzburgite-dunite through the transgressive dunite. The: lowest rocks in the mass, composed mainly of transgressive dunite, grade upward into the interlayered rock about 3,000 feet above the fault block base. The upper transgressive dunites tend to form interconnecting linear networks and probably a few pipe-like structures. The transgressive dunite is thought to have formed by action of water derived from the underlying sedimentary rocks; the water heated by the hot ultramafic rock (at the time of emplacement) altered the pyroxene to olivine and tal^c, and, with lowering temperature, to serpentine. Other interpretations are possible. Virtually all the chromite in the Jung Tor Ghar lies in or immediately above the masses of transgressive dunite. This fact provides a key to chromite exploration: The most favorable zone for prospecting lies in the vicinity of the upper contacts of the transgressive dunite masses where they are flatly dipping; if the transgressive dunite masses are steeply dipping'or pipe-like, the chromite tends to be more centrally located. The Jung Tor Ghar is believed to contain enough unmined chromite at practical minable depths to equal or exceed that mined to date but the individual deposits are likely to be small.

Mapping of Muslim Bagh ophiolite complex (Pakistan) using new remote sensing, and field data

“…The best preserved series of subophiolitic metamorphic rocks is located at the north-western side of the Jang Tor Ghar massif (Fig. 2) metamorphic sequences showing inverted metamorphic gradients (Rossman et al, 1971a;Munir and Ahmad, 1985;Mahmood, 1994 andMahmood et al, 1995). The series starts at the contact with peridotite-mylonites and garnet-amphibolites and grades downwards into amphibolites and fine-grained epidote amphibolites or epidote-actinolite-schists with inter layering of calcite.…”

“…More interest in detailed mapping and geological understanding of the area arose from its economic potential in high-grade chromite ore. Rossman et al (1971a) compiled preliminary maps of Muslim Bagh ophiolite. Rossman et al (1971b) also showed that the chromite deposits are located at the top of the dunite bodies which they called ''transgressive dunite''.…”

Chromite Deposits of Pakistan: A Short Review

“…It comprises of ultramafic rocks containing 80% of harzburgite and 20% of dunite; while the mafic deposits consist of gabbro with minor layers of serpentine. The ultramafic tectonites are comprised of <10% of dunite and >90% of the harzburgite [1,28].…”

“…Rossman and Abbas [28] reported that the chromite in the upper part of the complex is found in 3-4.5m thick and 2km laterally extending layers, irregular massive bodies of <1m2 thickness in the western part while podiform, massive and irregular along the sharp contacts such as Hiru Shah deposit [1]. Main deposits are located at BarjoKanri, Hiru Shah, LandiKand, Qila and Badasar.…”

Occurrences of rock-fulgurites associated with steel pylons of the overhead electric transmission line at Tor Zawar, Ziarat District and Jang Tor Ghar, Muslim Bagh, Pakistan

“…The surrounding area comprises outcrops of mafic and ultra-mafic rocks of the Jang Tor massif of the Muslim Bagh Ophiolites, which are part of the Bela-Waziristan Ophiolite Belt. It marks the western margin of the Indian plate with the Afghan block of the Eurasian plate (Hunting Survey Corporation 1961; Rossman et al 1971;Khan et al 2007); and is thought to be a relic of the Neo-Tethyan ocean floor obducted onto the Indian plate subsequent to closure of the NeoTethys and collision of the Indian plate with the Eurasian plate at the Cretaceous-Tertiary boundary or later in the Palaeocene-Early Eocene times (Allemann 1979;Sarwar 1992;Ahmed 1996;Gnos et al 1996).…”