Source component mixing controls the variability in Cu and Au endowment along the strike of the Eastern Andean Cordillera in Peru

作者：Angerer, Thomas^*; Kemp, Anthony I. S.; Hagemann, Steffen G.; Witt, Walter K.; Santos, Joao O.; Schindler, Christian; Villanes, Carlos

来源：Contributions to Mineralogy and Petrology, 2018, 173(5): 36.

DOI：10.1007/s00410-018-1462-5

• Continental arc magmatism
• U-Pb geochronology
• Whole rock geochemistry
• Hf-O isotopes
• Zircon trace elements

Mississippian arc magmatic suites of the Au-rich Pataz and Cu-dominated Montanitas regions in Peru reveal distinct modes of magmatic-hydrothermal petro- and metallogenesis. The distinction is remarkable due to their broad contemporaneity (336-322 Ma), arc-parallel position, and close distance (< 50 km) to each other. In both arc regions, petrography, geochemistry, and the tectonic setting of magmatic suites suggest a rapid switch from syn-collisional/compressional to post-collisional/extensional (with 'A(2)-type' signature) emplacement regime. Rocks of the Au-rich Pataz region originate from mixed sources with a contribution from the mantle (epsilon Hf > 0 and delta O-18 of similar to 5.3%) and assimilated old crust (variously low eHf and delta O-18 > 5.3%). The ultimate source of Au in the mineralised Pataz batholith was oxidised (fO(2) at FMQ buffer; based on zircon trace chemistry) and alkali-, LILE- and HFSE-enriched, most likely represented by the metasomatised mantle. The synextensional emplacement of the relatively reduced (Delta FMQ < 0), but unmineralised, A(2)-type suite involved assimilation of reduced crust. Associated, reduced, magmatic-hydrothermal fluids infiltrated the Au-bearing batholith suite and effectively mobilised and transported and concentrated Au. In the Montanitas region, rocks are oxidised (Delta FMQ > 0) and dominantly mantle derived without significant incorporation of crustal material. Samples from the Cu-mineralised suites indicate the additional contribution of a delta O-18 < 5.3% source, potentially melted layer-2 gabbro. In addition, the elevated whole-rock La/Yb and Sr/Y ratios are compatible with minor addition of slab-derived material, which may have enhanced Cu endowment in this region. Late-magmatic, oxidised fluids derived from the younger A(2)-type suite controlled Cu mobilisation and concentration, while Au behaved largely refractory. In general terms, it is postulated that source mixing in continental arcs is a first-order control of contrasting Cu and Au endowment and that sequential intrusion processes facilitate late-magmatic-hydrothermal mobilisation and concentration of specific metal assemblages.

• 出版日期2018-5