HIGH GRADE METAMORPHISM, REMOBILIZATION, AND POLYDEFORMATION OF THE BALMAT ZINC SULFIDE DEPOSITS, NW ADIRONDACKS, NEW YORK STATE

Zinc orebodies of the Balmat-Edwards district, NW Adirondack Lowlands of northern NY State, have long been famous for structural complexity induced by upper amphibolite grade metamorphism and polydeformation during the ca. 1.1 Ga Grenville Orogeny. Interpretations of recent geological mapping and diamond drilling results of the two newest orebodies at the Balmat mine reveal a fascinating geological history. Zinc ore was remobilized as syn-peak metamorphic anatectic sphalerite dikes differentiated from conformable, syngenetic, massive sulfide lenses. Sulfide dikes intruded laterally extensive macrofractures that cross-cut relict bedding and foliations in host marbles to form elongate secondary “daughter” orebodies that typically reach 6000 feet in length but which may extend to 14,000 feet. Much later, at lower temperatures, “top-side-east” ductile shear displacements partitioned along the original macrofracture surfaces imparted Durchbewegung textures to the transgressive daughter mineralization. As a result the once-contiguous “Mahler” and “New Fold” daughter orebodies are now separated by as much as 1000 feet. Subsequent nappe-scale folding inverted the Mahler and New Fold orebodies on the upper limb of the Sylvia Lake syncline. The very existence of these daughter orebodies mandates the presence of an as yet undiscovered primary massive sulfide source.