Nickel-rich chromian muscovite from the Indus suture ophiolite, NW Pakistan: Implications for emerald genesis and exploration

Abstract

Ubiquitous veins and stockworks of quartz traverse the ophiolitic emerald-hosting, carbonate-altered ultramafic rocks in the Swat Valley. Some of the emerald-bearing quartz veins contain chromian muscovite and tourmaline. In addition, veins and clusters consisting of chromian muscovite and/or tourmaline occur in zones of carbonate-altered rocks where the quartz veins are most abundant. The chromian muscovite is characterized by high Mg/Fe ratios (4-9) and contains variable and in some cases anomalously high concentration of Ni (ranging up to 9 wt% NiO). A detailed investigation reveals that the Ni and Mg entered the chromian muscovite structure as a part of a complex coupled substitution: . The stable coexistence of quartz, chromian muscovite, tourmaline and emerald suggests that all these phases are cogenetic and precipitated from Si-rich, Al-, Be-, B-and K-bearing fluids related to a single episode of hydrothermal activity. The Mg, Cr and Ni contents in chromian muscovite were most probably extracted by the percolating hydrothermal solutions from the host carbonate-altered ultramafic rocks through wall rock reaction. The observed high variability in the Mg, Cr and Ni contents of chromian muscovite probably reflects low mobility of these elements during the hydrothermal process or a result of local equilibrium under relatively low T conditions.

Chromium- and nickel-rich micas and associated minerals in listvenite from the Muránska Zdychava, Slovakia: products of hydrothermal metasomatic transformation of ultrabasic rock

“…or older Ni-rich sulphide minerals (probably pentlandite) could have served as a principal source of Ni in the micas. Analogous partial dissolution and replacement of primary chromite by Cr-Ni-rich muscovite was documented in listvenitized ultrabasic rock from Swat Valley, Pakistan (Arif and Moon 2007).…”

“…% NiO (0.53 apfu), together with up to 13.5 wt. % Cr 2 O 3 (0.75 apfu); it occurs in quartz veins and stockworks that traverse the ophiolitic emerald-hosting, carbonatealtered ultramafic rocks in the Swat Valley, the Indus suture, NW Pakistan (Arif and Moon 2007). Nickel-rich phlogopite (up to 4.3 wt.…”

Petrogeochemistry of listvenite association in metaophiolites of Sahlabad region, eastern Iran: Implications for possible epigenetic Cu–Au ore exploration in metaophiolites

“…5a, b and c) of three powdered listvenite samples, the most frequent minerals include quartz, magnesite, dolomite, calcite, serpentine, chromite and fuchsite. The peak positions for fuchsite, chromite and serpentine were checked with standard JCPDS card and are very similar to those detected by Arif and Moon (2007) for fuchsites associated with magnesite bearing chromite from the Indus suture ophiolites.…”

Paragenesis of Cr-rich muscovite and chlorite in green-mica quartzites of Saigaon–Palasgaon area, Western Bastar Craton, India

“…In most of the quartzites worldwide, occurrence of a variety of minerals such as zircon, rutile, tourmaline, Cr-spinels, pyrope, sphene, magnetite, hematite, chlorite, biotite, pyrophyllie, andalucite, silliminite, kyanite, corundum, microcline, epidote, and zoicite have been reported (Whitemore et al 1946;Clifford 1957;Ramiengar et al 1978;Raase et al 1983;Sinha-Roy and Ravindra Kumar 1984). Two types of origins are commonly envisaged for the formation of green-mica quartzites, namely: hydrothermal alteration, in which, mica is formed either due to replacement of pre-existing rocks or due to hydrothermal solution emanating from magmatic intrusions (Whitemore et al 1946;Geijer 1963; Morata et al 2001;Arif and Moon 2007) or by metamorphism of chromium-rich minerals in the source rock (Leo et al 1965;Argast 1995). Green mica quartzites are known to occur in Archaean rocks, e.g., Montana, USA (Heinrich 1965), Outokumpu, Finland (Treloar 1987), Dharwar Craton, India (Argast 1995).…”