At Whisky Hill, a mill of forty stamps has been set up which is now running with satisfactory returns. The cost by contract of delivery of the ores to the mill, being stated at forty cents (40c.) per ton, the cost of mining and treatment in mill being considerably less, it is said, than one dollar per ton, the amount treated being five tons to each stamp.
The chemical results of the extensive decomposition of metallic sulphids which has in former times occurred at these localities, offer an interesting problem in chemical geology. The sulphur has been removed chiefly as sulphuric acid beyond doubt, which has combined with iron and copper to form sulphates of these metals. These have for the most part disappeared, being washed out by the atmospheric waters, and have followed the drainage of the country. At Whisky Hill I found the sulphate of iron, (Coquimbite) sulphate of copper, (Cyanosite) and alum. The water of the shaft contains copper enough to redden the iron tools. At Quail Hill considerable masses of heavy spar are found, formed probably from the action of soluble sulphates upon witherite. No gypsum was observed at either locality.
The mineral species observed at Whisky Hill, are as follows:
- Metallic Gold.
- Metallic Copper.
- Metallic Silver.
- Red Copper.
- Malachite (Green Carbonate of Copper).
- Azurite (Blue Carbonate of Copper).
- Chrysocolla (Silicate of Copper).
- Cyanosite (Blue Vitriol).
- Copper Glance (Vitreous Copper).
- Zinc blende.
- Galena.
- Iron pyrites.
- Alum.
- Coquimbite.
- Heavy Spar.
- Hematite (chiefly the earthy varieties).
- Kaolin.
- Lithomarge and various aluminous and magnesian silicates resulting from the decomposition of the chloritic and talcose rocks.
The list of species is about the same for the deposit at Quail Hill.
The line of division between the ore-bearing ground in these great ore channels, and the country rock is quite distinctly seen on both the eastern and western outcrop at Quail Hill, and on the western at Whisky Hill. At the former place it is a dark bluish porphyritic rock, probably metamorphic, of a sandstone or silicious sediment. The outcroppings resemble those of many quartz veins, and I find the moss-covered portions of this quartzose matter full of cavities, resulting from the decay of pyrites, and yielding, by assay, three to five dollars to the ton in bullion.
From all the evidence presented, we seem justified in regarding these remarkable metallic deposits as segregated veins, holding a pretty uniform and high tenor of gold and silver, associated with and derived from the decomposition of extended masses of metallic sulphurets and quartzose matter, and carrying at times, ores of copper, the commercial value of which is, however, entirely subordinate to that of the precious metals which are found to characterize these veins or ore channels.
San Francisco, April 15th, 1867.
Mr. Falkenau read a communication “On the Spirit of the Age and its Influence in the Department of the Natural Sciences.”