Hao et al. (2019) Platinum-Group Element Geochemistry of the Escondida Igneous Suites, Northern Chile: Implications for Ore Formation, Journal of Petrology, 60, 487-514, doi:10.1093/petrology/egz004. < 20191211105631-169391 > pub

Map on Earth or stone. Places and analyses are shown.

  • abstract:

    Platinum-group element (PGE) geochemistry may be used to constrain the timing of sulfide saturation in magmas, which influences the Cu and Au fertility of evolving magmatic systems. We report new geochronological and geochemical data, with emphasis on PGE geochemistry, for a suite of regional porphyritic hornblende–diorite intrusions and ore-bearing porphyries from the super-giant Escondida and smaller Zaldivar Cu deposits of Northern Chile. The regional dioritic intrusions have zircon U–Pb ages between 39.6 to 37.1 Ma, which overlap with the ages of the ore-bearing Escondida and Zaldivar porphyries (38.1 to 35.0 Ma). Whole-rock major and trace element, and Sr–Nd–Pb and zircon O–Hf isotope geochemistry indicate that the regional diorites and ore-bearing porphyries are co-magmatic and originated from the same mantle-derived magma by fractional crystallization, with minor contamination by Paleozoic crust (∼10%). The low concentrations of PGE in the regional diorites show that they reached sulfide saturation before the MgO content of the melt fell to 4.7 wt %, the MgO content of the most primitive sample analysed. The fraction of sulfide melt which separated from the melts that formed the regional diorites is estimated to be ∼0.12 wt %; this resulted in the partitioning of highly chalcophile elements (Au and PGE) into a sulfide phase that was retained in cumulus rocks at depth. However, the fraction of sulfide melt was too low to have a significant effect on the Cu content of the fractionating melt. As a consequence, when the evolving melt eventually reached volatile saturation, it contained enough Cu (40 ± 10 ppm) to form a super-giant Cu deposit. In contrast, Au was largely stripped from the melt by sulfide precipitation, with the result that the mineralization at Escondida is Cu dominant, with only minor Au. The Zaldivar deposit, on the other hand, contains even less Au, which is attributed to a longer fractionation interval between sulfide and volatile saturation. This study provides evidence to support previously proposed models which suggest that the timing of sulfide saturation, the amount of sulfide melt produced, the water content and oxidation state of the melt, and the magma volume are critical factors in determining the potential to form a porphyry Cu deposit. Plots of Pd/MgO against Y can be used as empirical indicators of magma fertility for porphyry mineralization, and to discriminate between Cu–Au and Cu-dominated systems, but cannot predict the size of the deposit. The super-giant status of the Escondida deposit is attributed to it being underlain by a large batholith with a calculated minimum mass of 1012 tonnes (∼400 km3).

  • doi: 10.1093/petrology/egz004
  • modified at 2020-07-30
1: IM69 2: IM59 3: IM10 4: IM8 5: IM119 6: ESC2 7: ESC3 8: ZAL1 9: ZAL4


(a) Sr isotopes_procedures of Yoshikawa and Nakamura (1993) on TIMS Thermo-Fisher MAT262
(b) Nd isotopes_procedures of Nakamura et al. (1991, 2003) on TIMS Thermo-Fisher MAT262
(c) Pb isotopes_procedures of Kuritani and Nakamura (2002, 2003) on TIMS Thermo-Fisher MAT261
1: IM119 2: IM8 3: IM10 4: IM59 5: IM69 6: ESC2 7: ESC3 8: ZAL1 9: ZAL4


(a) LA-ICP-MS on ICPMS
1: IM119 2: IM8 3: IM10 4: IM59 5: IM69 6: ESC2 7: ESC3 8: ZAL1 9: ZAL4


(a) ICPMS on ICPMS
Tixhr1582241917 thumb IM119 < 20170303143253-903779 >pub
  • IGSN: IEDRM011T
  • place: S24°9′40.2″, W69°5′33.3″ more
  • classification: igneous
  • physical-form: powder
  • quantity (g): 9.62875
  • age (Ma): 37.59 (0.33)
  • description: Escondida district; dacite
  • modified at 2020-01-06
Tixhr1653927954 thumb IM59 < 20170303143514-102444 >pub
  • IGSN: IEDRM011Z
  • place: S24°11′25.4″, W68°57′59.5″ more
  • classification: igneous
  • physical-form: powder
  • quantity (g): 12.23769
  • description: Escondida district; diorite
  • modified at 2020-01-06
Tixhr1819703570 thumb IM8 < 20170303144159-647839 >pub
  • IGSN: IEDRM011X
  • place: S24°13′5.1″, W68°57′26.7″ more
  • classification: igneous
  • physical-form: powder
  • quantity (g): 13.64667
  • age (Ma): 38.72 (0.5)
  • description: Escondida district; diorite
  • modified at 2020-01-06
Tixhr 714601161 thumb IM10 < 20170303144340-822351 >pub
  • IGSN: IEDRM011Y
  • place: S24°12′37.3″, W68°57′40.0″ more
  • classification: igneous
  • physical-form: powder
  • quantity (g): 14.55903
  • age (Ma): 37.07 (0.63)
  • description: Escondida district; diorite
  • modified at 2020-01-06
Tixhr 159585031 thumb IM69 < 20170303144517-964764 >pub
  • IGSN: IEDRM0120
  • place: S24°10′51.6″, W68°57′48.1″ more
  • classification: igneous
  • physical-form: powder
  • quantity (g): 13.05864
  • age (Ma): 39.62 (0.43)
  • description: Escondida district; diorite
  • modified at 2020-01-06
Tixhr 2057726075 thumb ESC2 < 20170303144652-350126 >pub
  • IGSN: IEDRM011U
  • classification: igneous
  • physical-form: powder
  • quantity (g): 12.94059
  • age (Ma): 37.92 (0.44)
  • description: Escondida district; ore-bearing porphyries; dacitic quartz-feldspar porphyry
  • modified at 2020-01-06
Tixhr 1001036878 thumb ESC3 < 20170303144817-390074 >pub
  • IGSN: IEDRM0121
  • place: S24°15′33.7″, W69°4′55.1″ more
  • classification: igneous
  • physical-form: powder
  • quantity (g): 10.25209
  • age (Ma): 37.19 (0.44)
  • description: Escondida district; ore-bearing porphyries; dacitic quartz-feldspar porphyry
  • modified at 2020-01-06
Tixhr804538966 thumb ZAL1 < 20170303144938-572903 >pub
  • IGSN: IEDRM011V
  • place: S24°12′50.2″, W69°3′44.6″ more
  • classification: igneous
  • physical-form: powder
  • quantity (g): 12.05865
  • age (Ma): 38.06 (0.52)
  • description: Escondida district; ore-bearing porphyries; Zaldivar deposit; dacitic quartz-feldspar porphyry
  • modified at 2020-01-06
Tixhr 939642561 thumb ZAL4 < 20170303145107-305345 >pub
  • IGSN: IEDRM011W
  • classification: igneous
  • physical-form: powder
  • quantity (g): 7.95308
  • age (Ma): 37.11 (0.37)
  • description: Escondida district; ore-bearing porphyries; Zaldivar deposit; dacitic quartz-feldspar porphyry
  • modified at 2020-01-06
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IM119 pub TIMS Thermo-Fisher MAT262 3 20191211143005-010789
IM119 pub ICPMS 2 20191211120848-025872
IM119 pub TIMS Thermo-Fisher MAT261 6 20191211143026-684143
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IM59 pub TIMS Thermo-Fisher MAT262 3 20191211143004-400104
IM59 pub ICPMS 3 20191211120850-354659
IM59 pub ICPMS 36 20191211114143-051821
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IM59 pub TIMS Thermo-Fisher MAT261 6 20191211143026-691275
IM8 pub ICPMS 36 20191211114140-560767
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IM10 pub ICPMS 5 20191211120849-290618
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ESC2 pub TIMS Thermo-Fisher MAT261 6 20191211143026-351497
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ESC3 pub ICPMS 4 20191211120852-598174
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ESC3 pub TIMS Thermo-Fisher MAT262 4 20191211143015-564381
ESC3 pub TIMS Thermo-Fisher MAT262 3 20191211143005-595395
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ZAL1 pub ICPMS 36 20191211114148-646657
ZAL1 pub ICPMS 4 20191211120853-886688
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ZAL1 pub TIMS Thermo-Fisher MAT262 4 20191211143015-258243
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ZAL4 pub ICPMS 6 20191211120853-201234
ZAL4 pub TIMS Thermo-Fisher MAT262 3 20191211143005-284337
ZAL4 pub TIMS Thermo-Fisher MAT262 4 20191211143015-448291
ZAL4 pub TIMS Thermo-Fisher MAT261 6 20191211143027-817626
name spots global-id
caption ID rowname stone
Table 4 Sr–Nd–Pb isotopic compositions for the regional diorites and ore-bearing porphyries from the Escondida district pub 20191211150336-592504 Sr-Nd-Pb-isotopes (Hao et al., 2011) 9
Table 2 Whole-rock trace element concentrations (in ppm) for the regional diorites and ore-bearing porphyries from the Escondida district pub 20191211115521-346598 trace (Hao et al., 2019) 9
Table 3 PGE and Re concentrations for the regional diorites and ore-bearing porphyries from the Escondida district pub 20191211121643-029322 PGE (Hao et al., 2019) 9
manual
  • name
  • Hao, Hongda
  • Campbell, Ian H.
  • Richards, J.P.
  • Nakamura, E.
  • Sakaguchi, Chie