New York Mountain, Alma, Alma Mining District, Park County, Colorado, USAi

Regional Level Types
New York Mountain	Mountain
Alma	Village
Alma Mining District	Mining District
Park County	County
Colorado	State
USA	Country

New York Mountain is a small hill, indicated on the topographic map by a closed contour, 3,400 feet southeast of Mosquito Peak. An escarpment bounds it on the northeast, but the slopes are gentle in other directions. Beds just below the top of the Leadville limestone crop out at the peak and form virtually a dip slope to the southwest.

The entire output from New York Mountain has consisted of silver-lead ore occurring as replacement deposits in the Leadville limestone. To judge from the extent of the workings, between 100 and 300 tons has been mined, mostly from a single stope directly beneath the peak. Weakly mineralized rock of the same type as the ore is fairly widespread. Unproductive quartz veins of the London type are said to have been cut in the Finnerty tunnel and the Little Newton shaft, on the northeast slope of the mountain.

Sphalerite, less abundant galena, and minor amounts of pyrite and chalcopyrite are the only sulphide minerals identified megascopically in specimens collected from mine dumps and from surface exposures, but others may have existed in the ore. These minerals form isolated irregular-shaped or somewhat rounded clusters that range in size from mere specks to masses having a diameter of nearly 2 inches. Unreplaced Leadville limestone is the chief gangue constituent in all specimens, but its relative abundance varies greatly. An iron-bearing dolomite is usually about as abundant as the sulphide minerals; it forms small vuggy masses, some of which surround the sulphide clusters. Calcite occurs locally. Quartz is rare where sulphide minerals are abundant, but local areas of silicified limestone are found in the general vicinity of the ore. Small amounts of travertine and limonite are sufficiently widespread to suggest that the ores were slightly oxidized.

Microscopic examination of a polished section from one of the specimens reveals, in addition to the minerals seen megascopically, small amounts of a "gray copper" mineral (tetrahedrite, tennantite, or freibergite), with insignificant amounts of a supergene lead mineral (anglesite?) and covellite. The sequence pyrite (oldest), sphalerite, "gray copper," galena is indicated by the grain boundaries; the relative age of the chalcopyrite could not be determined, although it probably followed sphalerite. Veinlets of sphalerite healing cracks in a few pyrite grains show that slight brecciation intervened between the periods of deposition of these two minerals. All or nearly all of the white dolomite was formed after the galena. In spite of its rather dark megascopic color, the sphalerite is a variety low in iron, and it is free of chalcopyrite blebs.

Although the available specimens came only from material having no commercial value, they yield sufficient information to indicate that the ore bodies on New York Mountain were very similar in type to those at the Russia mine, described in a previous paper. However, on New York Mountain the ore bodies are smaller and less numerous, barite is absent, and the Leadville limestone is less silicified facts all of which indicate less intense mineralization than at the Russia mine.