Page 91 - Handbook of Gold Exploration and Evaluation

72 Handbook of gold exploration and evaluation

north Central America, was caught in the middle between the two halves of
Rodinia. Collision between the three continental masses about 550 million years
ago (mya) resulted in the Pan-African orogeny and the formation of a
supercontinent called Pannotia. These collisions took place when the continents
comprising Pannotia already had active rifting.

Pannotia
Pannotia was the name given by Ian W.D. Dalziel in 1997 (see the Encyclopedia
Wikipedia) to a hypothetical supercontinent that existed from about 600 mya to
about 540 mya. Pannotia broke up at the end of the Precambrian and the
Palaeozoic era began 540 mya with four continents, which lined the equator
between latitudes 60ë N and 60ë S:
· Gondwana (which was composed of Antarctica, Australia, India, South
America and South Africa)
· Baltica (northern Europe)
· Laurentia (North America)
· Siberia.

Polar regions were apparently land free.
Similarities in the patterns of Proterozoic mineralisation appear to reflect the
amalgamation of northern Australia with Laurentia during the early Proterozoic
(Hoffman, 1989). Barley and Groves (1992) record other important metallogenic
events associated with the African continent. These events include the Bushveld
Complex (platinum group elements) and the Palabora carbonatite (Cu-Fe-P).
The Palabora deposits were emplaced at around 2 billion years ago (bya) within
a piece of continental crust that had been only slightly affected by orogenic
activity since the late Archaean (Gustafson and Williams, 1988). Volcanogenic
massive-sulphide and mesothermal gold mineralisation also occurred in opiolite
and island arc terrains accreted to a peripheral Pan-African orogen (900±600
mya) in the Arabian-Nubian shield (Al-Shanti, 1979).

2.1.4 Phanerozoic eon (580mya±present)
The Palaeozoic era (225±580 mya) of the Phanerozoic eon was characterised by
reduced physical changes and abundance of sedimentary rocks; geological
periods were separated on the basis of intervals of continental uplift followed by
submergence and encroachment of oceans onto the land. Polar regions during
the Ordovician period (490±475 mya) were wide expanses of ocean and land-
masses were located around the equator. Baltica and Gondwanaland shifted to
the east and south. The Caledonian Orogeny reached its peak during the Silurian
period (435±430 mya). The sequence of continental collisions and the formation
of the supercontinent Pangaea resulted from: