Diamond zone is much wider than believed: River Krishna downstream of Prakasam Barrage in Vijayawada may contain diamonds: Area extends up to the offshore of the Krishna river

Syed Akbar
Hyderabad:  After oil and natural gas, the offshore of Krishna
River now holds prospects for diamond mining. The diamond search in
the State has extended to areas beyond Vijayawada and up to the
estuary of the river Krishna with the Geological Survey of India
finding evidence for the presence of precious stones in this hitherto
unexploited region.

So far, the area between Sangam (confluence of Tungabhadra and Krishna
in Mahbubnagar district) and Prakasam Barrage in Vijayawada is
recognized as the diamond zone. Recent studies by the GIS have
revealed that the diamond zone well extends beyond Vijayawada and up
to near shore in Avanigadda and Nagayalanka in Krishna district and
Repalle in Guntur district. Penna River, downstream of Somasila, is
another new area with prospects of diamond reserves. The region may go
well into the sea, offshore of Krishna and Penna.

The mapping of the geological terrain of coastal areas dating back to
the last glacial maximum (18,000 years ago) and beyond shows that the
palaeo-channels and channel bars comprising diamond bearing gravels
extend into the lower part of the Krishna delta and even into the near
shore area.

According to GSI, about 18,000 years ago Krishna as well as the Penna
rivers had extended courses joining the sea at lower levels. “The
palaeo-channels of Krishna and Penna in their delta and offshore areas
may also form important diamond prospects, in select zones,” GSI’s new
“Quaternary Maps” point out. Quaternary is the current period in the
Cenozoic era on the geological timescale. These diamonds were formed
during this period. Diamond-bearing gravels are also found in Chennuru
and Kanuparthy, located along the upper reaches of the Penna.

GIS believes that Quaternary studies of the river basins of Penna,
Hagari and Handri might help in delineating their palaeo-drainage
channels and in locating new diamond bearing terrace/gravel zones. The
existence of a few old pits and dumps near these gravel beds indicates
that terrace gravels were excavated to recover diamonds in the past.

Diamond constitutes the most important economic mineral of the Quaternary
fluvial gravels of AP. The alluvial tracts around Kolluru, Ustapalle,
Paritala, Chandralapadu and Venkatayapalem areas in Guntur and Krishna
districts along the banks of the Krishna River, have yielded many
world famous diamonds.

Besides diamonds, precious stones like transparent to translucent ruby
corundum have been found around Salebhanjar village in Khammam
district. Corundum is also found in an area of about 50 sq km up to
Lalguda in the south, Tummalapalle in the west and Lallurgudem in
Kadapa district.

Gem variety garnets are noticed in the Muneru river around Tekugudem.
Semi-precious stones including chalcedony, agate, carnelian, jasper
and opal have been found in abundance in the older gravel bed as well
as recent channel/ point bars of the Godavari river around Bhadrachalam.