The Jabal Bitten quadrangle covers an area of 2833 sq km in the
eastern part of the Precambrian Shield in Saudi Arabia. The rocks in
the quadrangle are divided geographically alone arcuate north-trending
lines into an eastern area of granite intruded by a swarm of dikes of
rhyolite and andesite, and a western area of dominantly pelitic
chlorite-sericite schist, separated by the narrow central complex of
the Idsas Range. This complex is composed of pyroclastic rocks, lava,
conglomerate, marble, and plutonic mafic rocks that have been intricately modified by episodes of metamorphism, igneous intrusion, and
faulting. The Idsas Range contains ancient gold and copper mines,
and deposits of magnetite, copper, asbestos, and chromite.
The rocks in the Jabal Bitten quadrangle are here interpreted to
consist of three major sedimentary and volcanic groups, the lowermost
of which was deposited unconformably on hornblende-biotite granite
gneiss, and all of which are intruded by granite dikes and plutons.
From oldest to youngest the layered rocks are called Halaban Group,
Bi'r Khountina Group, and Murdama Group, A biotite-hornblende granite
is older than uppermost Bi'r Khountina, and peralkalic granite is
younger than Murdama.
The layered rocks of these groups are generally metamorphosed to
the greenschist facies. The metamorphic grade rises abruptly at the
Idsas Range to the albite-epidote-amphibolite facies and lower subfacies of the amphibolite facies in parts of the Halaban Group; some
skarn east of the range may be in the upper part of the amphibolite
facies. Characteristically, the Halaban Group has the highest grade
and the greatest range in metamorphic grade, and the Murdama Group
has the lowest but most uniformly developed metamorphic grade. The
metamorphism of the rocks was caused by three successive pulses of
regional dynamothermal metamorphism plus contact metamorphism around
the younger bodies of plutonic igneous rocks.
Four major structural elements of the quadrangle are reflected
in the geography and geologic units. These are a mantled gneiss dome
on the east separated from a north-plunging synclinorium in rocks of the Murdama and Bi?r Khountina Groups on the west by a narrow dejective zone of the Halaban and lower Bi?r Khountina. The dejective zone is much modified by impricate overthrusts and accompanying tear faults. These major faults have pushed elements of the Halaban and Bi?r Khountina westward over Bi?r Khountina and Murdama, with the result that very complex fault patterns have evolved.
Open geochemical reconnaissance of the area disclosed one positive anomaly for nickel and 40 threshold indications of several elements, principally nickel, chromium, copper, and tungsten. Heavy-mineral and radiometric reconnaissance showed 18 areas containing scheelite and/or powellite and four areas of anomalous radioactivity. Most of these features are in the dejective zone, as are five of the nine ancient workings, the massive and disseminated magnetite, most of the secondary copper minerals, and the traces of asbestos, magnesite, and chromite known in the quadrangle. The mantled gneiss dome and a complex of gabbro and amphibolite on its southwestern flank are the next most mineralized areas. Scant evidence of mineralization is present in the Murdama Group west of the dejective zone.
Magnetite deposits at Jabal Idsas have the greatest potential of the mineral deposits in the Jabal Bitran quadrangle. Further study of gold at Fawara and Selib mines is recommended, as is investigation of a positive nickel anomaly that shows threshold cobalt and above background radioactivity. The garnetiferous skarn in the east-central part of the quadrangle should be examined for composition and abrasive character of the garnet and for the remote possibility of tungsten in scheelite and beryllium in helvite.
Additional Publication Details
USGS Numbered Series
Reconnaissance geology of the Jabal Bitran quadrangle, Kingdom of Saudi Arabia