Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/447

1869.] LE NEVE FOSTER-CARATAL GOLD-FIELD. 337 It was only on the north side of the Yuruari, near the Tupuquen Ford and north of Callao, that I noticed outcrops of a rock which I have called "gabbro" on the authority of Mr. David Forbes, F.R.S.

To the north of the mining district—in fact, in the country about Upata, gneiss, mica-schist, hornblende-schist, and granite occur; but time did not permit my making any full examination of this part. It will thus be seen that to the west and north the gold-bearing slates are surrounded by gneiss and other metamorphic rocks. No fossils have as yet been found, though carefully searched for by Dr. Plassard ever since he discovered the gold-fields. The age of the rocks is consequently unknown.

I will now pass on to the gold deposits of the Caratal district.

These may be classed under four heads: — 1. Lodes, veins, "reefs," or "ledges," filones; 2. Alluvial or "placer" diggings, or greda; 3. Red earth, or tierra de flor; 4. Gravel and sand of river-beds.

1. Lodes. — About a dozen lodes have been discovered and worked on. It is impossible to give any general direction of the strike and dip of these lodes; but it may be remarked that several well-marked and rich lodes run east and west, while others, equally productive, have strikes approaching to north and south.

As the lodes are few in number, a short description of each will furnish the easiest method of giving an idea of their general nature.

The Callao lode lies about a mile and three-quarters N.N.W. of Nueva Providencia. It is a north and south lode dipping west, and is from 1 foot to 2 feet thick in many places; it consists mainly of quartz with a little iron-pyrites and brown oxide of iron, &c., and a few blackish streaks due, perhaps, to chlorite. The gold in this lode is very coarse, and specimens of pure white quartz and native gold, without a particle of oxide of iron, are often found. The surrounding rock or "country," is felstone, with a little iron pyrites. The miners say that the presence of iron pyrites is a favourable sign for the productiveness of the lode. The Callao lode has been worked along the strike for a distance of about 200 yards, and it is said to die out southwards. The deepest workings in the Caratal district are upon this lode; but they only reach down 36 yards, further progress being prevented by water and the want of pumping-machinery. Very large quantities of gold (I believe I am under the mark in saying 1000 oz. per month) have been obtained from Callao.

The Corinna lode is situated further eastward, on the bank of the Yuruari. The lode is 4 feet wide in places, and dips west. It consists mainly of quartz, with brown oxide of iron, mammillated pyrolusite, thin streaks of a blackish mineral, and visible gold. This lode has been worked to a depth of about a dozen yards and has been profitable.

In the neighbourhood of the Corinna the American Company has made openings upon other lodes and branches. Some of the quartz shows visible gold, the rest does not; but all is auriferous; on an average, I am told that the quartz from these openings gives about 1-1/2 oz. of gold to the ton. The "country" of these lodes and of