Page 93 - Handbook of Gold Exploration and Evaluation

74 Handbook of gold exploration and evaluation

2.5 Pangaea after rifting (Wilson, 1976).
activity, commenced to break up. Oceans opened and closed. Laurentia split up
into North America, Greenland and Europe and that part of Asia north of the
Indian sub-continent. Sediments now in the Caledonian-Hercynian-Appalachian
Mountains of Eastern Europe were laid down in an old ocean in the lower
Palaeozoic. This ocean may have been closed long before the present Atlantic
Ocean opened up and separated the Appalachian Mountains from their
continuation in north-eastern Europe less than 150 million years ago (Bullard,
1969). In the Cainozoic period (65 million years to the present) the continents
drifted to the positions they occupy today. North America is joined to South
America through the Isthmus of Panama, the Indian landmass has continued its
northerly drift and has collided with Asia, and Greenland has been detached
from Europe and Asia by the mid-Atlantic rift.
The greatest abundance of sediment-hosted Pb-Zn and Cu minerals deposited
during the formation of Pangaea (300±250 mya) appears to have been in either
epi-continental or foreland settings of the Caledonian-Appalachian Orogen, e.g.
Duane and DeWit (1998). Most types of gold deposits, including volcanic
hosted massive sulphides, podiform chromite porphyry style Cu and Mo
mineralisation occur in island arcs and basins along the Pacific margin
(Sawkins, 1990).
Peripheral orogeny and related mineralisation is thought to have occurred
along a continental margin from southern California to Scandinavia. Mineral-
isation includes Archaean style mesothermal Au (e.g. Homestake), VHMS and
porphyry Cu deposits (see also Gaal and Gorbatchev, 1987). High sea levels