New Mexico Mineral Symposium — Abstracts

The Organ district has long been known to contain tellurium mineralization associated with base-metal sulfides. The tellurium minerals, occurring as carbonate replacements in favorable beds, are confined generally to areas in the district where galena is the primary ore mineral. The minerals occur as discrete, macroscopic grains and as inclusions in other sulfide minerals, usually galena or sphalerite. Interestingly, tellurium mineralization appears to be confined to areas above 6,000 ft elevation (except at the Memphis mine where tetradymite is reported in the Roos workings). A short description of the individual minerals and their mode of occurrence in the district follows:

ALTAITE (PbTe)--a white-gray mineral that usually occurs as cleavage masses associated with black shale contacts and with tremolite where it is paragenetically earlier than the sulfides. Microscopic grains have been observed in galena and sphalerite and associated with pyrite. Common in the Hilltop mine, reportedly with native tellurium.

RICKARDITE (Cu₃Te₂)--occurs as a purple metallic mineral (similar to tarnished bornite) when observed macroscopically (rare) with pyrite and sphalerite. Reported at Hilltop mine and most common at the eastern-most of the Rickardite claims. Occurs occasionally as microscopic inclusions in sphalerite. It is recognized by its fire-orange reflections with crossed polars under reflected light.

TETRADYMITE (Bi₂Te₂S)--fairly common with sphalerite and galena at the Memphis mine. Occurs as microscopic inclusions in galena and sphalerite at other deposits where it is galena-white and anisotropic under reflected light. It is the most widely distributed telluride in the district where it also occurs in veins along rhyolite dikes on the west slope of San Agustin Peak. Largest grains of the mineral occur in the Memphis mine as cleavage flakes or radiating masses.

Precious-metal mineralization occurs in the Little Buck workings associated with high-tellurium assays. A quartz-gold orebody is reported in the Hilltop mine. No precious-metal mineral phases have been recognized other than isolated occurrences of free gold. Precious-metal telluride systems are notable for their wide variety of telluride mineralogies. The presence of gold and silver tellurides is suspected and attempts to document these minerals are underway. Tennantite was observed at the Little Buck (new occurrence for this mine) and is considered a potential precious-metal phase.

Tellurium mineralization is associated most commonly with silicified zones that resemble hot-spring deposits. Preliminary fluid-inclusion homogenization temperatures in this quartz fall between 230 and 240 degrees C. Sulfide zoning appears opposite that suggested by earlier workers in the district. The accepted zoning pattern is concentric (Cu-Zn-Pb) from the Organ batholith. The recent recognition of a porphyry copper deposit north of the town of Organ provides a better "center" or source of the mineralizing fluids and, correspondingly, zoning appears best reconciled in an opposite direction than previously postulated. The distribution of tellurium mineralization can also be used to define distal zoning along with proximal porphyry-skarn zoning. The origin of the tellurium and precious-metal hot-spring system may be: 1) part of the porphyry copper-skarn system, 2) superimposed on the porphyry-skarn system as a retrograde phase of that mineralization, or 3) a completely different mineralizing event.