Heavy Mineral Investigations in the Siwaliks of Mohand, District Saharanpur, Uttar Pradesh, India

The Mohand anticline located south of Dehra Dun (U.P.) exposes the middle and upper Siwaliks (Sarmatian to Cromarian). The lower Siwalik was encountered in a deep well, a little south of Mohand.

The middle and upper Siwalik sediments are classified into two (A and B) and three (C, D and E) groups respectively on the basis of heavy mineral suites. The suite of group A consists of garnet, tourmaline, epidote, staurolite, and kyanite besides minor quantities of sphene, rutile, chloritoid, and monazite, and fairly abundant ore minerals (magnetite, hematite, limonite, pyrite and chromite?). Kyanite is marker for group A. Addition of hornblende to the above assemblage marks the suite of group B, and that of hornblende and sillimanite, the suite of group C. The suite of group D is characterized by flooding of ore minerals,. impoverishment of nonopaque minerals, very low garnet and very rare kyanite, and rounded zircon as well as tourmaline. The suite of group E is comparatively richer than that of group D. It mainly consists of very low garnet, rare but persistent sillimanite and abundant kyanite.

The absence of mineral markers in older rocks e.g., that of sillimanite in middle Siwalik and kyanite in lower Siwalik does not seem to be a function of intrastratal solution effects. Alternatively, it is concluded that their appearance was due to uplift and successive unroofing of more metamorphosed rocks constituting the provenance.

The heavy mineral suite of Siwaliks exposed along the Himalayan foothills vary from area to area. The suite of lower Siwalik extending from Jammu to eastern Uttar Pradesh is characterised by presence of staurolite marker and is similar throughout and consitutes a terrigenous mineral super-province. The suite of middle Siwalik sediments varies from area to area and the diversities are ascribed to splitting of the super-province into three provinces extending from Jammu to the Yamuna river, the Yamuna river to the Ganga river, and the Ganga river to Mithawali fault. The mineral province extending from Jammu to the Yamuna river gave rise to two sub-provinces extending from Jammu to the Markanda river and the Markanda river to the Yamuna river during the deposition of upper Siwalik sediments. The respective provinces are delimited by faults presently occupied by the Markanda, Yamuna and Ganga river courses. Tectonic activities along these faults in relation to post-Miocene, Himalayan orogeny vis-a-vis evolution of Siwalik lithotypes requires detailed analyses and, together with the recognition as well as definition of provinces, appears a necessary prerequisite for attempting any regional correlation on the basis of heavy minerals.

The heavy mineral suites of Siwalik rocks exposed in Mohand Anticline are not wholly comparable to those of Jammu, Punjab and Tanakpur (U.P.).