Portal de Periódicos da CAPES

Mineral Resources

2023; Springer Nature; Linguagem: Inglês

10.1007/978-981-99-1843-0_2

2198-3542

Ashoka G. Dessai,

Geological Studies and Exploration

The mineral resources of the State are hosted by the metasedimentary rocks which rest over the Anmode Ghat Trondhjemite Gneiss (3.4–3.3 Ga) and the intrusive Canacona Granite (2.9–2.3 Ga) together forming the basement for the supracrustal rocks. The volcano-sedimentary assemblage belongs to the 'Castlerock Band' which comprises two greenstone sequences, a lower metavolcanics-dominated sequence comprising the Barcem Group and a clastic-dominated sequence assigned to the Ponda Group. The banded iron formations (BIF) which have supported the State economy for over seven decades occur as bands, reefs and lenses of banded-haematite-quartzite (BHQ) and banded-magnetite-quartzite (BMQ) interstratified within the phyllites of the Bicholim Formation. The associated manganese ores, however, occur within both the quartz-sericite-chlorite schists of the Barcem and the pink ferruginous phyllites of the Ponda Group. The bauxite deposits are largely confined to the Mopa-Verna tableland (palaeoplain) which consists of a thick carapace of laterite capping various other lithologies. The bauxite mineralization occurs within the lower horizons of the laterite profile. The most widespread and better developed soil profiles occur on the coastal plain (< 10 m above MSL) where they have developed over coastal alluvium and granitic gneisses. In southern parts of the State, they are found to occur over laterites that cap the schistose metasediments. Sand extraction is largely 'in-stream' extraction confined mainly to the estuaries and in a few cases upstream sections of the major rivers. As for the marine shell deposits, the best and the largest occurrence of shells is located between Chopdem and Tuem in the bed of River Chapora. Two horizons of shells (0.5–0.7 and 0.3 m thick) occur within a shell-siltstone. It is exposed on the tidal/mud flat and extends laterally from 300 to 600 m; however, the continuity needs to be ascertained by pitting. These resources provide a means of livelihood to the local community.