Determining the absolute duration of magmatic-hydrothermal events leading to the formation of porphyry systems (i.e., including porphyry copper, skarn, and epithermal deposits) is one of the key questions in ore geology. This is so because the duration of magmatic-hydrothermal events in porphyry systems is instrumental to the development of genetic models necessary to explore a category of mineral deposits that provide most of the copper and significant amounts of base and precious metals to our economy. The problem of determining the absolute duration of magmatic-hydrothermal events in porphyry systems has been addressed through ther- mal modeling of cooling intrusions and time needed to precipitate specified metal amounts from active hydro- thermal systems with known metal concentrations and fluid fluxes. Both these methods have shown that the likely duration of hydrothermal systems is on the order of a few tens of kilo-annum (ka). Isotopic dating in con- trast is the only possible way to determine the life span of magmatic-hydrothermal events in fossil porphyry sys- tems. Analytical and methodological developments during the last decade in the fields of the most robust iso- topic systems commonly used for absolute dating (U-Pb, 40Ar/39Ar, Re-Os) allow us to date minerals with internal precisions <0.2% (2σ). For a 10-Ma-old mineral this corresponds to a <20-ka uncertainty, which is mar- ginally sufficient to discriminate the duration of hydrothermal systems at the tens of kilo-annum scale. How- ever, many geochronological studies on fossil porphyry systems have shown that these are most often formed through repeated cycles of several intrusion events, which extend the overall life of the porphyry systems to a few 0.X and up to ~2 Ma in some cases. Internal precisions of the above mentioned dating methods allow us, in theory, to comfortably discriminate events at the 0.X scale and the combination of U-Pb, 40Ar/39Ar, and Re- Os geochronology is a tool widely used by ore geologists to bracket the duration of cyclic magmatic-hydro- thermal events in porphyry systems. In this review we discuss some fundamental problems that are systematically overlooked in most geochrono- logical studies trying to bracket the life span of porphyry systems. We show that if these problems are not adequately taken into account and tackled the result will be that fundamentally wrong life spans of porphyry sys- tems will be estimated. We also provide basic guidelines to follow when trying to resolve the duration of mag- matic-hydrothermal events in porphyry systems with the highest accuracy and precision currently achievable

Natural processes driven by heat flow can be understood using quantitative reconstruction of the thermal history of accessory and common minerals that were formed or modified in these processes. Thermochronology assumes that isotopes are lost from minerals by thermally-activated volume diffusion, and forms the basis of many studies of the thermal evolution of the crust. However, some studies challenge this assumption and suggest that the mechanisms controlling isotope transport in minerals over geological time-scales are dominated by aqueous fluid flow within mineral pathways. Here, we test these contrasting hypotheses by inverse modelling apatite uranium–lead (U–Pb) dates to produce theoretical t–T solutions assuming Pb was lost by volume diffusion. These solutions are compared with independent geological constraints and intra-grain apatite U–Pb dates, which demonstrate that volume diffusion governed the displacement of Pb. This confirmation, combined with an inverse-modeling procedure that permits reheating and cooling paths to be distinguished between ∼375 and 570 °C, provides geologists with a unique tool for investigating the high-temperature thermal evolution of accessory minerals using the U–Pb method

We investigated the Neoproterozoic-early Paleozoic evolution of the Gondwanan margin of the north-central Andes by employing U-Pb zircon geochronology in the Eastern Cordilleras of Peru and Ecuador using a combination of laser-ablation-inductively coupled plasma-mass spectrometry detrital zircon analysis and dating of syn- and posttectonic intrusive rocks by thermal ionization mass spectrometry and ion microprobe. The majority of detrital zircon samples exhibits prominent peaks in the ranges 0.45-0.65 Ga and 0.9-1.3 Ga, with minimal older detritus from the Amazonian craton. These data imply that the Famatinian-Pampean and Grenville (= Sunsas) orogenies were available to supply detritus to the Paleozoic sequences of the north-central Andes, and these orogenic belts are interpreted to be either buried underneath the present-day Andean chain or adjacent foreland sediments. There is evidence of a subduction-related magmatic belt (474-442 Ma) in the Eastern Cordillera of Peru and regional orogenic events that preand postdate this phase of magmatism. These are confi rmed by ion-microprobe dating of zircon overgrowths from amphibolite-facies schists, which reveals metamorphic events at ca. 478 and ca. 312 Ma and refutes the previously assumed Neoproterozoic age for orogeny in the Peruvian Eastern Cordillera. The presence of an Ordovician magmatic and metamorphic belt in the north-central Andes demonstrates that Famatinian metamorphism and subduction-related magmatism were continuous from Patagonia through northern Argentina to Venezuela. The evolution of this extremely long Ordovician active margin on western Gondwana is very similar to the Taconic orogenic cycle of the eastern margin of Laurentia, and our fi ndings support models that show these two active margins facing each other during the Ordovician