Gt. Hill et al., Geochemistry of southwestern New Mexico fluorite occurrences implications for precious metals exploration in fluorite-bearing systems, J GEOCHEM E, 68(1-2), 2000, pp. 1-20
Fluorite-bearing Cu-Au, Ag-Au, and Ag-Pb-Zn deposits comprise a geologicall
y and genetically varied group of mineral deposits in southwestern New Mexi
co. Additionally, several small to moderate tonnage former fluorite orebodi
es and numerous non-economic fluorite occurrences are distributed throughou
t much of New Mexico, western Texas, and northern Sonora, Mexico. We differ
entiate fluorite-bearing deposit types utilizing variations in fluorite geo
chemistry. Several types of data were collected by fluid inclusion microthe
rmometry, delta D and delta(18)O analysis of inclusion fluids, and trace el
ement analysis of fluorite separates. Fluid inclusion microthermometry indi
cates that fluorite in most of the veins formed from low salinity (0-7 eq.
wt.% NaCl) fluids at temperatures between 100 degrees and 220 degrees C. A
small number of vein and replacement deposits hosted by limestone or granit
e, including the Hansonburg Mississippi Valley Type (MVT) deposit, and the
Zuni Mountains deposits, formed at similar temperatures, but from moderatel
y saline (10-20 eq. wt.% NaCl) fluids. Magmatic fluids (>600 degrees C, 80
eq. wt.% NaCl), are trapped in fluorite veins in the Capitan pluton. delta
D and delta(18)O values of inclusion fluids range, respectively, from -108
to -27 parts per thousand and from -9.9 to 7.3 parts per thousand relative
to SMOW. Horizontal to subhorizontal trends in delta D versus delta(18)O sp
ace suggest that variably-exchanged meteoric waters were responsible for fl
uorite deposition in most deposits. Trace elements show a broad range in co
ncentration from tenths to hundreds of parts per million. The sediment-host
ed fluorites in this study tend to have low Sigma REE concentrations relati
ve to fluorite hosted by igneous rocks. Limestone-hosted fluorites associat
ed with felsic intrusive rocks have high Sigma REE concentrations relative
to all other sediment-hosted fluorites. Signatures indicative of precious m
etals mineralization are present in low-salinity epithermal systems contain
ing Au and/or Ag. These are characterized by small and/or isolated ranges i
n Sr concentrations, Sc/Eu ratios, (Tb/Yb)(n) ratios, and Eu anomalies. Two
apparently barren fluorospar districts in southwestern New Mexico contain
fluorite with signatures indicative of precious metals mineralization and,
therefore, it is suggested that precious metals mineralization may also be
present within these districts. (C) 2000 Elsevier Science B.V. All rights r
eserved.