Mineral Veins.
Quartz veins deposited by solutions[136] in cracks and fissures of the igneous and metamorphic rocks are very numerous and widely distributed, especially in the Sukari district. They vary immensely in size, from mere strings to veins two metres or more in thickness; they cut the rocks in every direction and at every angle of dip. Steeply inclined veins are by far the most numerous, but some have a flat inclination and are then styled “reefs” by the miners.
The principal interest attaching to the quartz veins is the fact that they frequently contain gold, though seldom in particles visible to the unaided eye. The quartz veins were worked for their gold by the ancients, the remains of whose dwellings and stone grinding pans are found at numerous places, as for instance in the Wadi Hangalia, at Kurdeman, near Gebel Sabahia, at Gebels Sukari and Allawi, in the Wadi Lewewi, and at Romit and Darahib. Our modern prospectors have found these ruins of ancient mining camps and grinding pans to be the best guide to auriferous veins, gold being seldom found except in and near the old workings. As mentioned on [p. 27,] the ancients worked the mines by convict labour, and they could for that reason afford to work ores which are too poor to pay under modern conditions. But in certain cases the veins have been found rich enough to give possibilities of a commercial return to modern mining enterprise; a list of the prospecting licences and mining leases now in force is given on [p. 28.] As to the source of the gold, it is not known whether it came up in solutions from below, or has been secreted laterally from the country rock.
Besides gold, some of the quartz veins contain traces of copper, but none of the occurrences of copper ore within the area specially treated of in this book appear to be capable of yielding any considerable quantity of the metal, most of them in fact being mere stains due to oxidation and carbonatisation of traces of sulphides.[137]
Calcite veins are much more rarely met with than those of quartz. In only one of the veins I have examined is calcite present in any considerable quantity, namely in the vein of the old gold mines of Romit. In this vein, white to brown crystalline calcite is found mixed with chalybite, limonite, and smoky quartz [12,105 and 12,141], the last-named only being apparently auriferous. There did not appear to be enough chalybite and limonite in the vein to make it worth following up for iron ore, especially in view of the expense of transport from the place.
Magnesite and asbestos veins occur in the serpentines of the Gebel Gerf district. These occurrences, which appear not to be large enough to be worth working, have been described on [p. 330.]
[134]The figures in square brackets in this and the preceding chapter are the numbers under which the specimens are registered in the Geological Museum, Cairo.
[135]See Barron and Hume’s “Eastern Desert.” Cairo, 1902. p. 263.
[136]Other quartz veins which probably originated in quite a different manner are treated of under the heading of Igneous Rocks see ([p. 266]).
[137]The copper smelted in ancient times at Kubban, on the east bank of the Nile opposite Dakka, in latitude 23° 10′, was possibly obtained from mines at Abu Seyal (sometimes misspelt Absciel), north of the Wadi Alaqi in latitude 22° 47′, longitude 33° 44′, where there are extensive old workings, Abu Seyal lies outside the region described in this volume; a reference to the mines will be found in the Report of the Egyptian Department of Mines for 1906, p. 34.
CHAPTER XI.
TECTONICS AND GENERAL GEOLOGY.