The green mineral, so far as I can ascertain, has never been described, although it has often been noticed. It has been called by some, nickel gymnite, and I have once distinguished it by this name in a mining report. But this is a misnomer which I take this occasion to correct; nickel gymnite of Genth, found at Texas, Penna., is a hydrous silicate of magnesia, lime, and nickel. The species so characteristic of certain portions of the mother vein is anhydrous, and contains no nickel.
Mariposite (Provisional Name). Before the blowpipe it yields evidence of the presence of the protoxides of iron, lime, magnesia, and potassium; of the sesquioxides of chromium and aluminum with carbonic, silicic, and sulphuric acids. The oxide of manganese and sulphuric acid exist only as traces. The mineral is probably new, and must be referred to the mica section of an hydrous silicate. Should it, on a careful chemical examination, prove to be new, I would suggest the name Mariposite as an appropriate name for it, as it was on the Mariposa estate that it first attracted my attention, and where it exists in great abundance.
This species which is so characteristic of the mother vein, in connection with magnesian or chloritic rocks, occurs nowhere so far as I have observed in this vein when it is inclosed in argillites or syenites.
Of sulphides occurring in the mother lode there are two classes which deserve special mention, beside the ordinarily occurring pyrites of iron and copper.
These are the (1) antimonial copper sulphides, and the (2) antimonial lead sulphides; both are arsenical and are rich in both gold and silver.
To the first class allusion has already been made in the former part of this paper. Besides the Rawhide Mine, they are found in most of the openings on Whisky Hill, in Tuolumne County, in the Silver, App and Josephine, and Pine Tree Mines. The lively stains of blue malachite, seen at Williams’ Mine, on Whisky Hill, and occasionally elsewhere, are derived from atmospheric decomposition of the antimonial copper sulphides. The blowpipe detects the presence of iron, antimony, arsenic, copper, sulphur, tellurium (in certain cases) sulphur, gold and silver. The vein is so abundant as to give to the raw ore, in some cases, magnetic properties; and the button from the blowpipe assay becomes strongly magnetic.
The antimonial lead sulphides occur in considerable abundance at the Trio Claims, on Whisky Hill. The appearance of this ore recalls that of granular galena. The gold and silver value of this ore is very high, but no portion of it can be saved by the ordinary mechanical treatment with mercury. The blowpipe detects the presence of antimony, lead, iron, arsenic, sulphur, gold and silver. There is no trace of copper, and the quantity of arsenic present is slight. The ore is therefore essentially an antimonial lead sulphide, rich in gold and silver.
There is good reason to believe, that as this remarkable vein becomes more thoroughly explored, it will disclose other new or rare compounds containing gold, and that these already noticed will be found to be more widely diffused when proper care is applied to the study of the mineralogy of the lode.
In Amador County the mother lode is found in connection with argillaceous slates and syenite. Thus at the Eureka Mine, of Hayward, known as the Amador Mining Co., the vein has a soft, black slate for its foot wall and a heavy, firm syenite or greenstone (called granite by the miners) for the hanging wall. The mineralogy of the vein is extremely simple, being in fact nothing more than iron and copper sulphurets, chiefly the former, with rarely galena or blende. I sought in vain for any of the species mentioned in the former part of this paper. There are no magnesian minerals, and the Mariposite is entirely absent. The other mines of that range, as far as I examined them, all partake of the same simplicity in mineralogical character. There can be but little doubt, as it appears to me, that the inclosing rocks in each case exercise an important influence on the mineral contents of the vein.
San Francisco, December 2d, 1867.