Grasmere 1:100 000 Sheet, Home toa Few SurprisesMapping of the...

Grasmere 1:100 000 Sheet, Home to
a Few Surprises
Mapping of the Grasmere sheet near
Broken Hill was undertaken as part of
the Koonenberry Mapping Project, part
of the Exploration New South Wales
program. This sheet joins Bunda and
Kayrunnera as the third, first edition
1:100 000 scale map completed to date.
A further two maps, Nuchea and
onnaminta, are currently in progress
and the remainder of the outcropping
block is scheduled to be mapped at
1:100 000 scale. The Grasmere map
area is within the southern portion of
the outcropping Koonenberry Belt
which defines the eastern margin of the
Curnamona Craton in western NSW.
The belt is separated from the
outcropping Broken Hill Block by the
northwest striking Bancannia Trough,
containing up to 6 km of Devonian and
Mesozoic section. The Koonenberry
Belt consists of multiply deformed Late
Proterozoic and Cambrian sedimentary
and volcanic rocks with less deformed,
post Delamerian cover sequences that
range from Late Cambrian to
Cretaceous.
The recent mapping has
considerably extended the strike length
of the horizon prospective for Cu, Zn,
Ag and Au bearing massive sulphide
mineralisation at Grasmere. The
mapping has also located previously
undocumented shafts sunk into
carbonate altered mafic volcanic rocks,
and an undocumented shaft sunk into
gold bearing Devonian basal
conglomerate. The delineation of the
structural framework of the area also
offers new exploration possibilities.
While most mapping concentrated
on the Cambrian and older basement
rocks that host the Grasmere
mineralisation, examination of
Devonian strata revealed details of
faulting and the structural setting of the
shear controlled lode system up to 8 km in length
along the Koonenberry Fault.
Within both the Nuntherangie silver field and Wertago copper field, felsic volcanics and intrusions
are present and subsurface intrusions are postulated. The presence of felsic intrusions, numerous
historic mines and a favourable fault system suggest a prospective area for epithermal
mineralisation.