tions such as Paramount Canyon, the veins TaylorCreek tin distrisl- may reach three to four centimeters in width and a few meters in height and length. A dis- seminated cassiterite halo has been noted stratigraphy,structure, around the veins in Squaw Creek. A recently discoveredrhyolite porphyry has andtiming of mineralizationintensely altered the surrounding country rock near NM-59 where the road crossesthe Conti- byTed L. Egglestonand David L Norman,New Mexico lnstitute of Miningand Technology, Socorro, NM nental Divide. This porphyry is locally quartz- sericite altered and contains as much as I go pyrite. Similar intrusives have been mapped Introduction The Taylor Creek tin district is located in by Woodard (1982) southeast of the Taylor Primary tin depositscommonly are found in the north-central Black Range some 80 km Creek region. granitic plutonic environments where the tin west of Truth or Consequences,New Mexico occurs as cassiterite in greisen veins and as (fig. l). Cassiteritenuggets were first found in Regional geology disseminations in altered granite (Taylor, placers (Fries, 1940a). in the district in 1909 The tin-bearing Taylor Creek Rhyolite is 1979).In southwest New Mexico, however, tin Shortly wood tin thereafter, cassiterite and located in the Mogollon-Datil volcanic field, a occurs as cassiterite in hematite-cassiterite were porphyritic found in vein depositsin rhy- mid-Tertiary volcanic field consisting of inter- veins which cut Tertiary rhyolite domes and placer (Hill, olite lavas as well as in deposits mediate to felsic volcanic rocks and volcani- flows. This type of tin deposit has been re- l92l). Sincethat time, numerousauthors have clastic sedimentary rocks that unconformably ported at only two other localities in North reported geology, geochemistry, on the and overlie older rocks of various ages.In the Tay- America, Lander County, Nevada (Fries, potential economic of the area, among them lor Creek region, the volcanics overlie Paleo- 1942), and the State of Durango, Republic of (1940a,b), (1942), Fries Fries and others zoic limestones and clastic sedimentary rocks. Mexico (Foshag and Fries, 1942; Pan, 1914: (1972), (1976), (1978), Lufkin Coney Richter Overlying and interbedded with the uppermost Huspeni and others, 1982). These unique tin (1981), (1981). Correa and Goerold Sincethe volcanic rocks is the Gila group, a thick se- depositspresently are the focus of attention by pro- discovery of the tin deposits, the reported quence of coarse clastic sedimentary rocks. various mining concerns, the U.S. Geological placer duction from the depositshas been 9.85 The Gila group was deposited in basins result- Survey, and numerous university research (Volin tons of concentrate averaging 5090 tin ing from the formation of the Rio Grande rift groups. Studies by Charles Maxwell of the and others, 1947). Lode production has been and the Basin and Range province. U.S. Ceological Survey, John Lufkin of the minimal. The Taylor Creek region is part of the Colorado School of Mines, and these authors primary The tin veins consist of hematite Mogollon Plateau, a structurally simple block are aimed at defining the origin of various as- quartz, and cassiteritewith minor amounts of bounded on the west by the Clenwood graben pects of the tin mineralization. In addition, cristobalite, potassium- chalcedony, calcite, and on the east by the Winston graben, both Dave Harvey (University of Texas at El Paso) feldspar, (Lufkin, 1972; heulandite, and topaz of which are related to the Basin and Range is evaluating the economic potential of a por- Goerold, l98l). Theseveins generallyless are province and the Rio Grande rift. The region tion of the region. than wide. in loca- one centimeter but some is a westerly dipping monocline with numer- ous small unconformities suggesting that the central part of the Mogollon Plateau under- went minor subsidencefrom at least 33 m.y. to 2l m.y. ago. The Mogollon Plateauhas inter- acted with the extensional tectonism as an essentially coherent block. The entire block was downdropped, covered with Cila group sedimentary rocks, later /\ uplifted, and is presently being exhumed. The interior of the o lronMtn Slerr0 C0 uni y \ ALSOIN THIS ISSUE: AlamoBand Navajo Reservationcoal deposits p.5 Stephenson-Bennettmine p.9 9e"JD--Qft -'\ BluewaterLake State Park p.14 -_-.-...J , Service/News p. 16 1982mineral notes p.2O C(lMINGSOON FloridaMountains overthrust belt Uraniumproduction in NewMexico FIGURE l-LocATloN MAPoF TAYLoRCREEK REcloN (adapted from U.S. Geological Survey map of New Mexico at scaleof l:500,000). block, at least in the Taylor Creek region, Overlying the Hells Mesa tuff is an un- Kline Mountain. The source of the Stiver Can- underwent no significant faulting during the named, poorly to moderately welded, crystal- yon is unknown at this time. downwarping and subsequentuplift. poor, ash-flow tuff as much as 20 m thick. Lit- Several units overlie the tuff of Stiver Can- tle is known of this unit as it is poorly exposed yon at various places. These units include the Volcanic stratigraphy and apparently discontinuous, possibly filling rhyolite of Dolan Peak, the tuff of Kline The following descriptions are based on shallow paleovalleyson top of the Hells Mesa Mountain. and an unnamed red latite lava. field work which is part of the Ph.D. disserta- tuff. The tuff contains approximately 790 The red latite lava is less than 35 m thick and tion of the senior author. The regional map- phenocrysts of feldspar (6%o) and biotite consists of large potassium feldspars (up to 2 ping has been releasedas Open-file Report 177 (190). cm in length) in a red, lithoidal, fine-grained of the New Mexico Bureau of Mines and Min- The basaltic andesite of Poverty Creek (28 groundmass. The base of the unit is a flow eral Resources(Eggleston, 1982b). m.y.; W. E. Elston, 1982,personal communi- breccia; where the unit pinches out east of the The oldest volcanic rocks in the region are cation) consists of interbedded andesite and Continental Divide, a breccia carapace con- approximately 440 m of interbedded, inter- basaltic andesitelavas and brecciaswith green taining vitric clasts of the lava in a very fine mediate-composition lavas, breccias, and volcaniclastic sedimentary rocks separating grained breccia matrix was found. pyroclastic material. (Fig. 2 is a schematic many of the flows. The andesites are fine The tuff of Kline Mountain (new, informal stratigraphic section graphically displaying the grained and contain phenocrysts of pyroxenes name) pinches out against the red latite lava. stratigraphy and geologic relationships in the (?) that have altered to a brown claylike min- This unit is as much as 160 m thick (estimated) Taylor Creek region.) The lavas are andesitic eral. Quartz crystals are locally seen and are along the Continental Divide and pinches out to latitic and generally thin with brecciated- believed to be phenocrysts. Coney (1976) esti- southwest of Kline Mountain. The geometry flow tops and bottoms. Latitic ash-flow tuffs mated that the unit is in excessof 200 m thick. of the unit suggestsdeposition in a basin or are a minor constituent as are volcaniclastic Near the Kline Mountain rhyolite porphyry, broad paleovalley. The unit is a sequenceof sedimentaryrocks (Woodard, 1982).All of the the andesites have undergone mild to intense interbedded ash-flow and air-fall tuffs and units are laterally discontinuous. This se- propylitic alteration. The mildest alteration volcaniclastic sedimentaryrocks. The tuffs are quence has been called the Spears Formation produced epidote along joint surfaces, the crystal-poor to crystal-rich with variable pro- (Coney, 1976)and the Rubio Peak Formation most intense alteration produced a bleached portions of sanidine and quartz with traces of (Woodard, 1982), which are laterally equiva- rock with secondary epidote, calcite, and pos- biotite. The volcaniclastic sedimentary rocks lent. Using the nomenclatureof Osburn and sibly chlorite. Near the contact with the in- are tuffaceous sandstones, siltstones, and Chapin (1983,in press),these rocks are part of trusive, the andesites contain clay minerals pumice-bearing conglomerates.The upper few the Datil Group. The age of the Datil Group that may be due to mild argillic alteration. meters of the unit contain vitric clasts similar spans 37-33 m.y. (Elston and others, 1973; The tuff of Stiver Canyon overlies the basal- to the overlying rhyolite of Dolan Peak sug- Elston, 1976;Chapin and others, 1978). tic andesiteof Poverty Creek and is as much as gesting a genetic relation between the two The Hells Mesa tuff is as much as 150m of 200 m thick (Woodard, 1982). This tuff is units. Alteration related to the Kline Moun- crystal-rich, moderate to densely welded ash- poorly to moderately welded, crystal-poor to tain intrusive has been mild to intense. Near flow tuff erupted from the Socorro cauldron moderately crystal-rich, and white to buff in the contact with the intrusive, an advanced (Woodard, 1982; Eggleston, 1982a).The top color. The unit contains 1-liv/o phenocrysts argillic assemblageof alunite-silica-clayswas of the unit is characterizedby a thinly bedded, of sanidine, quartz, and coppery biotite. Sani- produced. Away from the contact, an argillic poorly to moderately welded tuff as much as dine is the dominant phenocryst with minor assemblageof clay (kaolin?)-silica-alunite was 30 m thick. This unit may representair-fall quartz and a trace of biotite. Pumice is not produced. This is the unit that was mined for and small-volume