Albitization at 1700 ± 2 Ma in the Sudbury – Wanapitei Lake area, Ontario: implications for deep-seated alkalic magmatism in the Southern province

Abstract

U–Pb geochronology of hydrothermal monazite in albitized rocks from two gold deposits east of the Sudbury complex indicates that albitization in the Sudbury – Wanapitei Lake area occurred at 1700 ± 2 Ma and was coeval with a period of granitic plutonism in the Southern structural province between 1750 and 1700 Ma.A variety of rare earth element (REE) minerals, such as two generations of hydrothermal monazite, bastnäsite, synchysite, and gadolinite were identified in the albitized Huronian sediments in the Espanola – Sudbury – Wanapitei Lake areas. The presence of these REE minerals, the extraordinary light rare earth element enrichment in rocks from the Sheppard gold property east of the Sudbury igneous complex and the elevated REE concentrations in some albitized rocks suggests that sodium-rich fluids may have been generated by carbonatitic or alkalic intrusions at depth.Gold mineralization occurs in rocks that have been altered by at least two different types of fluids: (1) peralkaline; Na–REE bearing and (2) low pH, Co bearing. The high Co content of most mineralized samples and the relatively weak correlation between Au and Na2O suggests that gold was probably concentrated to economic grade by the low pH, Co-bearing fluids. The spatial association of albite and gold suggests that the albitized rocks may represent earlier fluid conduits that were subsequently refractured and invaded by the mineralizing solutions.