Proceedings Chapter
Reference
Carbon and oxygen isotope records of fluid mixing and fluid-rock interaction in carbonates from the zinc-lead deposit of san vicente
(central peru)
SPANGENBERG, Jorge Enrique, et al .
SPANGENBERG, Jorge Enrique, et al . Carbon and oxygen isotope records of fluid mixing and fluid-rock interaction in carbonates from the zinc-lead deposit of san vicente (central peru). In:
Abstracts / International Mineralogical Association 16th General Meeting . [S.l.] : International Mineralogical Association, 1994. p. 388-389
Available at:
http://archive-ouverte.unige.ch/unige:154358
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CARBON AND OXYGEN ISOTOPE RECORDS OF FLUID MIXING AND FLUID-ROCK INTERACTION IN CARBONATES FROM . THE ZINC-LEAD DEPOSIT OF SAN VICENTE (CENTRAL PERU)
Spaneenhere J.l, Fontbote L.1, Sharp Z.D.2, and Hunziker J.2 (IDepartement de Mineralogie, Uni. Geneve, 2Jnstitut de Mineralogie, Uni. Lausanne)
Carbon and oxygen isotopic characterization of host and gangue carbonates were used to constrain the mechanism of ore precipitation in the Mississippi Valley-type Zn-Pb deposit of San Vicente. The ol3c and ol8o values were measured for different carbonate phases (see table) from samples taken at the San Vicente mine following a hierarchical sampling sheme.
Carbonate phase (n) Dark replacement dol., I (29) White sparry dolomite, II ( 115) Late filling dolomite, illd (10) Late filling calcite,
me
(25)Doi. replacing evaporite, EPd (7) Cal. replacing evaporite, EPc (11)
oBc ranges (%oPDB) . 0.5 to 2.5 -0.1 to 1.7 -0.3 to 1.1 -11.5 to 0.7
-0.4 to 1.0 -4.5 to 0.8
5180 ranges (%oPDB) -9.6 to -6.3 -11.8 to -7.3 -12.5 to -9.8 -15.1 to -9.1 -12.1 to -9.8 -16. l to -9.5 For a given carbonate generation no significant differences were observed between: 1) the three rnineralii.ed dolomite units, 2) different mantos in the same dolomite unit, and 3) samples from crosswise profiles perfonned at the same manto.
However significant isotopic variations were detected at the textural scale. T!le figure shows the distribution of the median isotopic composition of the carbonate phases in the ol3c vs. 5180 space.
In the dark replacement dolomite (DRD) increasing hydrothermal alteration is recognii.ed through increasing grain size between very fine- grained (lvO, fine
(10.
and fully recrystallii.ed medium-grained (Im) DRD. The hydrothermal alteration is rec-0rded by an isotopic shift towards lower 5l3c and 5l 8Q values (trend A in the figure).In the suhgenerations of the white sparry dolomite (WSD) the isotopic trend is inverse, towards heavier isotopic composition from tl towards t6 (trend B in the figure), where: tl =spots of WSD, t2 =fine veinlets of WSD, t3 =ordered bands of WSD, t4 =zebra texture, t5 = crosscutting veins ofWSD, and t6 = WSD in breccia Trend B corresponds to the isotopic shift towards heavier 513(: and 5180 values reflecting the evolution of the mineralizing fluid (e.g. parent fluid ofIItq by interaction with the host dolomite.
1
LateCillingdol.(Ill) t4 t5
1-.. 'tvr
( B _g. .. f6~£IA -~,
tl ... 4. Im \
31 D;7
~
Dark repl dolomite(IvCtoim)
·..;
dol. "'Whitesparry dolom.ite(II, t1 to t6)
-2 Late
rill
in g cal. ( IIl) Carbonate replacing evaporites (EP)-3 I>
~
-4.,__~~~~~~~~~~~~~~~~~--I
-13 . -12 -11 -10 -9 -8 -7 -6
5l80.%0PDB
Quantitative models of the 513(: VS. 5180 Covariations in the diffe;ent carbonate generations are in line with geological and petrographic observations. The precipitation of the syn- and post-ore carbonate generations (EP, II, ID) involve mixing of the native fonnational fluid (e.g. parent fluid of
IvO
with a hot acidicextraformational fluid. The isotopic evolution of the host dolomite and of the subgenerations of the white sparry dolomite are explained by interaction of the mineralizing fluid with the host carbonate and previously precipitated gangue carbonai.es.
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~'. 7 JUHi 1995
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