Greenland holds a secret beneath its icy surface.  The Black Angel deposit is a treasure trove of zinc and lead.  This deposit is not a recent occurrence.  It is a remnant from a time long past.  The mineralization happened around 1, 884 million years ago.  This was during the Paleoproterozoic era.  The mineralization process was complex.  It involved the movement of fluids and the interaction of various rocks.  The zinc and lead minerals were formed in carbonate rocks.  These rocks were part of the Karrat Basin.  The basin was rich in evaporites.  This mineralization happened around 1, 884 million years ago.  This was during a time of significant geological activity.  The activity was related to back-arc spreading.  This process occurred between 1, 900 and 1, 850 million years ago.  The mineralization predated the formation of the Rinkian foreland basin.  This basin formed between 1, 850 and 1, 800 million years ago.  The mineralization also predated a collisional stage.  This stage was part of the telescoping of the Rinkian and Nagssugtoqidian Orogens.  The orogens were active between 1, 830 and 1, 800 million years ago.  The formation of the zinc and lead minerals involved the replacement of clean carbonate rocks.  This process led to the precipitation of sphalerite.  Sphalerite is a zinc sulfide mineral.  The precipitation happened around 1, 884 million years ago.  The formation of epigenetic massive pyrite in the cap rock happened around 1, 828 million years ago.  This process may have been influenced by the lack of chemical reactivity of the cap rock.  The cap rock may not have been suitable for the pH-buffered conditions needed for zinc and lead mineralization.  The process may also have been affected by regional Rinkian metamorphism.  This metamorphism occurred between 1, 830 and 1, 800 million years ago.  The metamorphism and tectonic compression may have impacted aquifer permeability.  This would have affected the continued migration of brines.  The initial Os

i-pyrite

 ratio from isochron regression suggests a crustal origin for osmium.  This implies that other metals in the zinc and lead mineralization also have a crustal origin.  The Rae Craton basement rocks are the dominant source for these metals.  This is based on the Os

i-pyrite

 and δ

66

Zn

pyrite/sphalerite

 data.  However, there is a complementary contribution of zinc.  This zinc comes from Paleoproterozoic sedimentary carbonate.  The contribution is estimated to be between 12 and 24 percent.  This source of zinc is possible due to the high Na/Cl ratio in Paleoproterozoic seawater.  It is also possible due to the absence of zinc-based eukaryotic metabolism in the shallow marine environment.  The study of the Black Angel deposit provides valuable insights.  It helps understand the processes that led to the formation of zinc and lead mineralization.  It also sheds light on the geological history of Greenland.  The findings have implications for the exploration of similar deposits.  They also contribute to the broader understanding of Earth's geological evolution.

PALEOPROTEROZOIC ZINC LEAD DEPOSITS

Greenland's Ancient Zinc and Lead Treasure: A Deep Dive

Continue reading...