TY - JOUR
T1 - Age and sources of the ore at Tharsis and Rio Tinto, Iberian pyrite belt, from Re-Os isotopes
AU - Mathur, R.
AU - Ruiz, J.
AU - Tornos, F.
N1 - Funding Information:
Acknowledgments This work was partially supported through NSF grants EAR 9708361 and EAR 9725833. The analyses were Fig. 3 Simplified stratrigraphic column illustrating the possible radiogenic sources of Os for the Iberian Pyrite Belt. (Modified from Leistel et al. 1998) performed in the W.M. KECK laboratory for isotope geochemistry at the University of Arizona, which was built with funds from the W.M. KECK Foundation and the National Science Foundation. We thank Drs. Baker and McCandless for help in the laboratory and thoughtful conversations about the Re-Os system in these ores.
PY - 1999/11
Y1 - 1999/11
N2 - Re-Os isotopes were used to constrain the source of the ore-forming elements of the Tharsis and Rio Tinto mines of the Iberian Pyrite Belt, and the timing of mineralization. The pyrite from both mines has simila]r Os and Re concentrations, ranging between 0.05-0.7 and 0.6-66 ppb, respectively. 187Re/188Os ratios range from about 14 to 5161. Pyrite-rich ore samples from the massive ore of Tharsis and two samples of stockwork ore from Rio Tinto yield an isochron with an age of 346 ± 26 Ma, and an initial 187Os/188Os ratio of about 0.69. Five samples from Tharsis yield an age of 353 ± 44 Ma with an initial 187Os/188Os ratio of about 0.37. A sample of massive sulfide ore from Tharsis and one from Rio Tinto lie well above both isochrons and could represent Re mobilization after mineralization. The pyrite Re-Os ages agree with the paleontological age of 350 Ma of the black shales in which the ores are disseminated. Our data do not permit us to determine whether the Re-Os isochron yields the original age of ore deposition or the age of the Hercynian metamorphism that affected the ores. However, the reasonable Re-Os age reported here indicates that the complex history of the ores that occurred after the severe metamorphic event that affected the Iberian Pyrite Belt massive sulfide deposits did not fundamentally disturb the Re-Os geochronologic system. The highly radiogenic initial Os isotopic ratio agrees with previous Pb isotopic studies. If the initial ratio is recording the initial and not the metamorphic conditions, then the data indicate that the source of the metals was largely crustal. The continental margin sediments that underlie the deposits (phyllite-quartzite group) or the volcanic rocks (volcanogenic-sedimentary complex) in which the ores occur are plausible sources for the ore-forming metals and should constrain the models for the genesis of these deposits.
AB - Re-Os isotopes were used to constrain the source of the ore-forming elements of the Tharsis and Rio Tinto mines of the Iberian Pyrite Belt, and the timing of mineralization. The pyrite from both mines has simila]r Os and Re concentrations, ranging between 0.05-0.7 and 0.6-66 ppb, respectively. 187Re/188Os ratios range from about 14 to 5161. Pyrite-rich ore samples from the massive ore of Tharsis and two samples of stockwork ore from Rio Tinto yield an isochron with an age of 346 ± 26 Ma, and an initial 187Os/188Os ratio of about 0.69. Five samples from Tharsis yield an age of 353 ± 44 Ma with an initial 187Os/188Os ratio of about 0.37. A sample of massive sulfide ore from Tharsis and one from Rio Tinto lie well above both isochrons and could represent Re mobilization after mineralization. The pyrite Re-Os ages agree with the paleontological age of 350 Ma of the black shales in which the ores are disseminated. Our data do not permit us to determine whether the Re-Os isochron yields the original age of ore deposition or the age of the Hercynian metamorphism that affected the ores. However, the reasonable Re-Os age reported here indicates that the complex history of the ores that occurred after the severe metamorphic event that affected the Iberian Pyrite Belt massive sulfide deposits did not fundamentally disturb the Re-Os geochronologic system. The highly radiogenic initial Os isotopic ratio agrees with previous Pb isotopic studies. If the initial ratio is recording the initial and not the metamorphic conditions, then the data indicate that the source of the metals was largely crustal. The continental margin sediments that underlie the deposits (phyllite-quartzite group) or the volcanic rocks (volcanogenic-sedimentary complex) in which the ores occur are plausible sources for the ore-forming metals and should constrain the models for the genesis of these deposits.
UR - http://www.scopus.com/inward/record.url?scp=0033387332&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0033387332&partnerID=8YFLogxK
U2 - 10.1007/s001260050239
DO - 10.1007/s001260050239
M3 - Article
AN - SCOPUS:0033387332
SN - 0026-4598
VL - 34
SP - 790
EP - 793
JO - Mineralium Deposita
JF - Mineralium Deposita
IS - 8
ER -