New Mexico Mineral Symposium — Abstracts

Many aspects of the mineralogy of the Black Range tin district (BRTD) have been presented previously (Foord et al., 1985, 1986, 1988; Foord and Maxwell, 1987; Maxwell et al., 1986). We have now identified and/or characterized all of the remaining unknown minerals discussed in earlier communications. Additional unreported species undoubtedly are present and may be character¬ized in the future.

Table 1 lists the minerals identified from three separate localities and from the rest of the BRTD. Three mineral species new to science have been discovered: squawcreekite, (Fe,Sb,Sn,Ti)O₂, a member of the rutile group; maxwellite, CaFeAsO₄F; and the Ce-analogue of chernovite-(Y), CeAsO₄. Species new to the state of New Mexico include: gasparite-(Ce), CeAsO₄, chernovite-(Y), YAsO₄, and tilasite, CaMgAsO₄F.

Three different members of the durangite group, XY(AsO₄)F, all having the titanite structure, have been found in the BRTD: durangite (X = Na, Y = Al) (3 localities), tilasite (X = Ca, Y = Mg) (1 locality), and maxwellite (X = Ca, Y = Fe) (2 localities). Solid solution exists between all three members. Tilasite from vapor-phase altered rhyolite at Willow Springs Draw has the following composition:

(Ca_0.55Na_0.47)(Mg_0.48 Fe³⁺ _0.20Al_0.15Ti_0.14Mn_0.01 )(As_0.94 P_0.02)O₄F
This mineral has been found only at Willow Springs Draw. Titanite, also found only at Willow Springs Draw, occurs in miarolitic cavities along with diopside (var. salite), pseudo-brookite, and other minerals. The titanite crystals are euhedral, gem quality, red brown, and range from <0.1 to 1 mm in maximum dimension. Their composition is unusual compared to regular titanite (CaTiSi05). The content of Y + REE is about 9 wt. %, with Y being the most abundant single element (about 3% Y203). Both LREE and HREE are present. Other elements include (in wt. %): Al₂O₃ 1.8, Mn₂O₃ 1.0, Fe₂O₃ 7.3, ZrO₂ 0.1, Nb₂O₅ 1.6, WO₃ 0.5, ThO₂ 0.17, V₂O₃ 0.15, Sb₂O₃ 0.15, Ta₂O₅ 0.37, F 2.0. Crystallization of titanite of this unusual composition indicates the abundance of REE's and other incompatible elements in the late-stage vapor phase. This titanite composition (average of three samples) is similar to those reported from complex granitic pegmatites. Titanite in rhyolites is generally sparse because of lack of available Ca and Ti. Calcite has been found only in miarolitic cavities with the rhyolites.

The diopside occurring with the titanite is yellow orange, and the crystals are usually acicular, transparent, euhedral, and
may be several millimeters in length. The composition of the diopside i (Ca_0.93Na_{0. 16} )(Mg_0.70Fe_0.28Mn_0.06Ti_0.01)(Si_1.92Al_0.05)O₆.

Crystallization of tilasite-maxwellite preceded that of titanite and diopside. Crystals of tilasite-maxwellite are etched and corroded to varying extent. The later titanite and diopside may owe their origin, at least in part, to dissolution of the earlier tilasite-maxwellite.

Minor amounts of chevkinite, (Ce,Ca,Th)4(Fe²⁺,Mg)₂(Ti,Fe³⁺)₃ Si₄0₂₂ or perrierite, (Ce,Ca,Th)₄(Fe²⁺,Mg)₂(Ti,Fe³⁺)₃Si₄O₂₂, which are dimorphous, also have been found at Willow Springs Draw. The gray-brown crystals are as much as 0.2 mm in maximum dimension. This particular chevkinite-perrierite is somewhat unusual because of its high ZrO2 content (3.04 wt. %). The composition (average of 10 points on one grain) is:
(Ce_1.37Ca_0.72La_0.64Nd_0.59Pr_0.15Sm_0.09Th_0.08Gd_0.06Dy_0.04Er_0.03Lu_0.02) (Fe²⁺_1.61Mg_0.17Mn_0.06)(Ti_2.60Zr_0.30Al_0.19Nb_0.05W_0.01)Si_4.24O₂₂

Table 1. List of minerals from rhyolite-hosted tin occurrences in the Black Range Tin District.

* - mineral species new to science
+ - mineral new to state of NM
quartz, sanidine, hematite, and cassiterite are ubiquitous
cristobalite, tridymite, and pseudobrookite are common.

The REE arsenates (REEAsO₄) occur in the two different structural forms now known in nature: huttonite-monazite type and zircon type. Chernovite-(Y), YAsO₄, has the tetragonal zircon-type structure while gasparite-(Ce)t CeAsO₄, has the monoclinic huttonite-monazite type structure (Schwartz, 1963; Graeser and Schwander, 1987). Chernovite-(Y) and its Ce-analogue have been found at Paramount Canyon. The Y-analogue of gasparite-(Ce) has not been found and has never been synthesized. The zircon-type structure of the REEAsO₄ is more stable at higher temperatures than the huttonite-monazite-type structure. Significantly, YAsO₄ and CeAsO₄ both occur at Paramount Canyon in the tetragonal (chernovite) form only, while tetragonal chernovite-(Y) and monoclinic gasparite-(Ce) occur at Squaw Creek. Crystallization temperatures of the arsenates at Paramount Canyon are higher than the temperatures of the arsenates at Squaw Creek. Inversion of tetragonal CeAsO₄ to monoclinic CeAsO₄ has not been achieved experimentally but must occur based on the natural existence of both forms.

The gasparite-(Ce) at Squaw Creek contains about 1.3 wt. % CaO, with 4.3% ThO₂ substituting for the LREEs as well as about 6.1% P₂O₅ substituting for As. Chernovite-(Y) at Squaw Creek contains about 0.6% CaO, 0.3% SiO₂, 0.2% ZrO₂, 3.3% P₂O₅, and 2.8% ThO₂. The REE arsenates are the only minerals in the rhyolites found to contain major amounts of phosphorus. Apatite, the most common accessory mineral containing major P, is essentially absent.

The assemblages of minerals in the rhyolite-hosted tin occurrences of the BRTD indicate that deposition took place from high-temperature vapor-phase conditions down to ambient conditions with the majority of minerals being deposited from hydrothermal fluids.
 

References:

1. Foord, E. E., Hlava, P. F., Fitzpatrick, J. J., and Maxwell, C. H., 1988, Three new minerals from Squaw Creek, stolzite from Nugget Gulch, and tilasite from Willow Springs Draw, Black Range tin district, New Mexico (abs.): New Mexico Geology, v. 10, no. 1, pp. 19, 22.
2. Foord, E. E., Maxwell, C. H., and Oakman, M. R., 1986, Geology and mineralogy of the Black Range tin district, Sierra and Catron Counties, New Mexico, 7th IAGOD symposium, Lulea, Sweden (August 18-22, 1986). Terra Cognita, v. 6, no. 3, p. 528.
3. Foord, E. E., Oakman, M. R., and Maxwell, C. H., 1985, Durangite from the Black Range, New Mexico, and new data on durangite from Durango, and Cornwall: Canadian Mineralogist, v. 23, pt. 2, pp. 241-246.
4. Foord, E. E., and Maxwell, C. H., 1987, Mineralogy of the Black Range tin district, Sierra and Catron Counties, New Mexico (abs.): New Mexico Geology, v. 9, no. 1, pp. 20-21.
5. Graeser, Stefan, and Schwander, Hans, 1987, Gasparite-(Ce) and monazite-(Nd)--two new minerals to the monzaite group from the Alps: Schweiz. Mineral. Petrogr. Mitt., v. 67, pp. 103??113.
6. MaXwell, C. H., Foord, E. E., Oakman, M. R., and Harvey, D. B., 1986, Tin deposits in the Black Range district: New Mexico Geological Society, Guidebook to 37th Field Conference, pp. 273-281.
7. Schwartz, H., 1963, Die Phosphate, Arsenate and Vanadate der Seltenen Erden (The phosphates, arsenates and vanadates of the rare earths): Zeits. fur Anorg. Allgem. Chem., v. 323, pp. 44-56.