Geology and Genesis of the Cerro la Mina Porphyry-High Sulfidation Au (Cu-Mo) Prospect, Mexico

Abstract

The Cerro la Mina Au (Cu-Mo) porphyry-high sulfidation prospect is located in Chiapas State, southeastern Mexico, outside of the major metallogenic provinces of Mexico. The prospect is hosted by Pleistocene alkaline volcanic rocks of the Chiapanecan volcanic arc that formed in a complex triple-junction tectonic setting. Cerro la Mina's stratigraphy comprises pyroclastic flows that were intruded by monzodiorites and diorites at 1.04 ± 0.04 Ma (U-Pb, zircon), and that were overlain by debris flows and synvolcanic trachyandesite domes. The volcanic stratigraphy of Cerro la Mina is dominated by pyroclastic flows and rare basalts that are cut by the Cerro la Mina breccia pipe, a matrix-rich granular, vertically oriented, downward-tapering, polymict lithic rock unit that is host to all of the significant alteration and mineralization. A NW-trending sinistral wrench fault, which was active throughout the history of Cerro la Mina, is responsible for dismembering the prospect after mineralization. The magmatic hydrothermal system was composed of early porphyry-style potassic veins (quartz + K-feldspar ± biotite) and stage 1 pyrite that are preserved in clasts within the breccia pipe, suggesting that brecciation disrupted an embryonic porphyry system. Late potassic alteration occurred after the formation of the breccia pipe, as its matrix is strongly K-feldspar altered. Hydrothermal fluids then produced phyllic alteration composed of quartz, muscovite, illite, illite-smectite, and chlorite that is associated with stage 2 pyrite ± chalcopyrite ± molybdenite ± quartz veins. An unusual zoned pattern of advanced argillic-argillic alteration overprinted potassic and phyllic alteration. This zoning included a low-temperature (<110°C) halloysite + kaolinite that extends from 800 to 250 m below present-day surface and is deeper than higher temperature (>120°C) quartz + dickite ± kaolinite ± pyrophyllite ± alunite that occurs from 250 m to the present-day surface. The advanced argillic-argillic altered rocks host the most significant Au-Cu mineralization, which is associated with stage 3 marcasite, sphalerite, galena, and barite, and stage 4 arsenian pyrite ± enargite ± covellite. The magmatic hydrothermal system at Cerro la Mina began sometime between monzodiorite emplacement (1.04 ± 0.04 Ma; zircon U-Pb) and the precipitation of porphyry stage 2 molybdenite at 780 ± 10 ka (Re-Os). 40 Ar/ 39 Ar dating of biotite (689 ± 13 ka) records the age at which the hydrothermal system cooled below the biotite closure temperature of ~300°C and provides a maximum estimate for the onset of advanced argillicargillic alteration. Sulfur isotope results of sulfides (-2.5 to +4.9‰; mean +0.7‰; n = 20) and a sulfate (barite; +10.5‰; n = 1) suggest a magmatic source of sulfur for all four stages of mineralization. The lack of residual quartz, rare alunite, and anomalous halloysite-kaolinite alteration may be explained by the high acid-buffering capacity of alkaline volcanic host rocks, high CO2 contents of the alkaline magma, and/or potentially by a h...

Chemical and short‐wave infrared characteristics of white mica associated with the Gajah Tidur porphyry copper system at the deep Grasberg Cu—Au—(Mo) deposit, Indonesia

“…By comparison, white micas from the Pebble porphyry deposit largely have ISM values <1.0, except for a “sericite (minor pyrophyllite)” sample which reported an ISM value of 3.65 (Harraden et al ., 2013). As well as having generally much higher crystallinity and therefore higher formation temperatures than Pebble porphyry system white micas, MQP white micas have higher crystallinity than all white micas from the Cerro La Mina high sulfidation epithermal deposit whose ISM ratios are all <1.6 (Jansen et al ., 2017: Figure 6), and those reported from other epithermal vein gold deposits with ISM ratios <1.0 (Victoria; Chang et al ., 2011; Sinongduo; Guo et al ., 2020; Shihu; Yao et al ., 2021).…”

Using Mineral Chemistry to Aid Exploration: A Case Study from the Resolution Porphyry Cu-Mo Deposit, Arizona

“…6G-L). Halloysite is a low-temperature clay mineral and is commonly considered a near-surface supergene alteration feature (e.g., Hedenquist et al, 1998), but it has been detected at considerable depths in some porphyry systems where it is inferred to have a hypogene origin (e.g., Kyne et al, 2013;Jansen et al, 2017). The presence of halloysite in the deepest samples from drill hole RT006 at Resolution (Table 3; Figs.…”

Global Occurrence, Geology and Characteristics of Hydrothermal-Origin Kaolin Deposits

“…This region is known as a tectonically active and complex region along the Chiapanecan volcanic arc, and is also located at the junction of the North American, Caribbean and Cocos plates. The Quaternary stratigraphy of the Cerro la Mina area presents with pyroclastic flows at 1.04 ± 0.04 Ma (U-Pb, zircon) and volcaniclastic matrix-rich breccias that were invaded by monzodiorites, alkali intrusions and feldspar-biotite-phyric trachyandesites dome cross-cuts, which are interpreted to be a volcanic-hydrothermal breccia pipe [213]. The eruption of El Chichón volcano in 1998 ejected anhydrite-bearing trachyandesite pyroclastic material from the active volcano-hydrothermal system.…”

“…Ref. [213] classified the Cerro la Mina magmatic hydrothermal alteration systems, which are composed of (A) early porphyry-style potassic and late-potassic alteration which occurred after the formation of the breccia pipe, including quartz + K-feldspar ± biotite and pyrite, (B) phyllic alteration composed of quartz, muscovite, illite, illite-smectite, chlorite, calcite, gypsum and tourmaline, and is associated with pyrite ± chalcopyrite ± molybdenite found in veins, and (C) advanced argillic-argillic alteration overprinted potassic and phyllic alteration. The advanced argillic-argillic zone includes low-temperature (<110 • C) hypogene halloysite + kaolinite occurrences extending from 800 to 250 m and is deeper than higher-temperature (>120 • C) quartz + dickite ± kaolinite ± pyrophyllite ± alunite that occur from 250 m to the present-day surface.…”