Multi-stage ore forming history of the Variscan porphyry Mo-Cu-W Myszków deposit (Poland): Evidence from trace elements of pyrite

Four generations of pyrite (Py I-IV) from the porphyry-type Mo-Cu-W Myszków deposit are investigated using electron-probe microanalysis and laser ablation inductively coupled plasma mass spectrometry. Pyrite-I, representing skarn-forming stage of mineralization associated with magma intrusion activity, was formed in a relatively high-temperature environment. It has high contents of Co (up to 3966.11 ppm), Ni (up to 2552.62 ppm), Mn (up to 70.32 ppm), and Se (up to 103.94 ppm), but is depleted in As, Te, V, and devoid of Sb. Pyrite-II, representing the main hydrothermal stage of ore mineralization under the vigorous boiling conditions, contains elevated levels of Co (up to 1962.31 ppm), Ni (up to 1080.86 ppm), and Se (up to 153.03 ppm) with a high Se/Te ratio of 28.30. Pyrite-III, formed under vigorous to gentle boiling conditions, is also enriched in Co (up to 3312.65 ppm), Ni (up to 1469.09 ppm), Se (up to 184.24 ppm), and Te (up to 117.50 ppm), but depleted in As, Mn, V. The latest, low-temperature generation of pyrite, Py-IV is characterized by the highest contents of As (up to 3331.79 ppm), Mn (up to 141.91 ppm), the elevated levels of Te (up to 62.51 ppm), but depletion in Co, Ni, Se, V. Cu (mostly Py-I and Py-II), Pb (mainly Py-II and Py-IV), Bi (mainly Py-IV), Ag and Au (mainly Py-IV) are found as trace elements of solid micro-sized inclusions hosted by various generations of pyrite. The results of the study seem to demonstrate the sequence of metal precipitation in the ore system. At the relatively high-temperature conditions (the contact metamorphism down to hydrothermal stage), the deposition of Co, Ni, Mn, and later Se in pyrite occurred. Additionally, cobalt and nickel concentrations might suggest a contribution from magmas of mafic composition. Copper was mobilized and formed solid micro-inclusions in the host pyrite. Later, along with the evolution of the ore-forming system, and lower temperature rate, tellurium entered the structure of pyrite, when the redox condition temporarily changed from oxidizing to more reducing. With the further temperature drop and likely rising oxidation, arsenic entered the pyrite structure in the most recent episode of the main hydrothermal ore-mineralization stage. Also, the highest budget of Bi, Pb, and Ag with traces of Au was deposited as micro-inclusions in pyrite during this period. The concentration of these elements can be related to the same mechanism, as revealed by their positive correlations, i.e. Bi vs Pb in Py-IV (R = 0.95) Ag vs Pb in Py-IV (R = 0.94), Ag vs Bi in Py-IV (R = 0.97). © 2022