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90 GOLD '90
<br />Second, the fault zone at San Luia marks the
<br />zest edge of the San Luia basin. The proximity of
<br />this fault to the edge of the basin implies that it
<br />is a Neogene basin bounding structure as opposed to
<br />an eroded or reactivated Laramide throat fault.
<br />Third, beds and flows in the Santa Fe Formation
<br />within the Culebra reentrant dip 10-20 degrees to
<br />the northeast. These dips map be explained by a
<br />minor rotational component to normal faulting along
<br />the westerly dipping low-angle fault zone.
<br />Fourth. emplacement of mid-Tertiary felsite
<br />dikes and sills at the east edge of the San Luia
<br />basin ie apparently synchronous with low-angle
<br />faulting.
<br />We believe that local and regional geologic
<br />evidence indicate a mid-Tertiary extensional
<br />"detachment"-style origin for the fault zone at San
<br />Luis. Alteration and mineralization overprinting
<br />an cataclnetic textures indicate that ore
<br />depoeftfon was post-faulting, but there is evidence
<br />for at least minor post-mineral faulting ae well.
<br />Or181n of mineralization/alteration
<br />The origin of the mineralizing fluids
<br />reaponaible for the San Luis deposit ie poorly
<br />understood at present. Age determinations (K/Ar)
<br />on aericite altered felsite dikes at the deposit
<br />yield -24 Ha and it ie reasonable to assume that
<br />this ie close to the age of gold deposition. These
<br />age dates, and the association of gold with base
<br />metals, molybdenum, and fluorine, lead us to
<br />conclude that mineralization may have a genetic
<br />relation to mid-Tertiary magmatism. Felaite dikes
<br />are a possible magmatic link, but nowhere, to date,
<br />have the dikes been found to correlate with gold
<br />mineralization.
<br />Genetic model for the San Luis deposit
<br />Low-angle "detachment"-style faulting developed
<br />in the middle Tertiary in response to an elevated
<br />geothermal gradient along the Rio Grande rift zone.
<br />Small-volume feleic magmas were emplaced at shallow
<br />crustal levels at this time. Magmatic and/or
<br />thermally driven metalliferous fluids intersected
<br />the low-angle fault zone at San Luis and
<br />precipitated sulfides in the relatively low-
<br />preasure, low-temperature environment of the clay
<br />capped breccias. Syn- and/or poet-mineralization
<br />movement along the fault zone allowed for partial
<br />unroofing of the capping clay zone which was
<br />immediately buried by unconsolidated Santa Fe
<br />sediments. Erosion of the Santa Fe Formation in
<br />the structurally elevated, "failed" portion of the
<br />rift basin allowed for partial exposure of the
<br />deposit.
<br />ACKNOWLEDGEMENTS
<br />Deposit. F. Deakin and W. Lehman Were instrumental
<br />in helping delineate the ore body as currently
<br />defined. The geologic picture was assembled with
<br />the assistance of V. DeRuyter and J. Suthard. L.
<br />Vega provided us with many atimulatiag ideas and
<br />discussions. However. we accept reaponaibilty for
<br />the ideas presented in this paper. We would
<br />particularly like to thank Fred Reiabick of the
<br />Bottle Mountain Exploration Company and Cary Dodson
<br />of the Battle Mountain Cold Campeny for allowing ue
<br />the time to prepare this information.
<br />REFERENCES
<br />Deakin, F. A., and W. C_ Lehman, 1988, San Luis
<br />Protect, Coatilla County, Colorado. Final
<br />Exploration Report, unpublished company
<br />report
<br />DeRuyter, V., 1988. Geology of the San Luis Protect
<br />Gold Deposit, Costilla County, Colorado,
<br />unpublished company report
<br />Johnson, S. D., 1988, San Luis Pro.iect, Mineable
<br />Reserve Calculation Procedure and Reaulta.
<br />unpublished company report
<br />Jones, D. M., 1989. Application of Extended Q-Mode
<br />Factor Analysis to the ~;eochemiatry of
<br />Selected Drill Hole Intercepts of the San
<br />Luis Gold Deposit. Colorado, unpublished
<br />company report
<br />Keller, G.R., Cordell. L.. Dais, C.H.. Peeples.
<br />W.J., and White, G., 19F4, A Ceophveical
<br />Study of the San Luie basin: in New
<br />Mexico Geological Society Guidebook, 35th
<br />Field Conference, Rio Grande Rift: Northern
<br />New Mexico, pp.51-57.
<br />Lipman, P.W., Menhert, H.H., aad Nasser, C.W.,
<br />1986. Evolution of the Latir volcanic field,
<br />northern New Mexico. end its relation to the
<br />Rio Grande Rift, ae indi~sated by potasaium-
<br />argon dating: Journal of Geophysical
<br />Research. v,91, no.B6, p. 6329-6345.
<br />Simmons, V.M., 1979, The San [c.ia Valley, Pruett
<br />Publishing Co., Boulder, Colo., 193pp.
<br />Suthard. J. A.. 1988, Silica Vein Studv,
<br />unpublished company report
<br />Tweto, 0., 1979, The Rio Grande rift system in
<br />Colorado: in Riecker, R.E. (ed.), Rio Grande
<br />rift--tectonics and maematism: American
<br />Geophysical Union. Washington. D.C., pp.35-
<br />56.
<br />Upson, J.E.. 1939. Physiographlc: subdivisions of
<br />the San Luis Valley, southern Colorado:
<br />Journal of Geology, v.47, pp.721-736.
<br />Many Battle Mountain Exploration Company and
<br />Battle Mountain Gold Company personnel contributed
<br />to our current understanding of the San Luis
<br />
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