HIGH GRADE METAMORPHISM AND REMOBILIZATION OF ZINC OREBODIES IN THE BALMAT-EDWARDS DISTRICT, NORTHWEST ADIRONDACKS, NEW YORK STATE

The Balmat-Edwards zinc mining district of northern New York State hosts mid-Proterozoic zinc orebodies metamorphosed to near granulite facies during the Grenvillian Orogeny about 1.1 bya. Mobile fractions of massive sulfide “parent “ orebodies locally remobilized into large-scale impinging macrofractures at ~700˚ C and 6 1/2 kb. “Daughter” remobilizates formed thin, extensive, transgressive sheets of nearly monomineralic sphalerite up to several feet thick. Thicker portions of the sheet like daughter orebodies form linear “footprints” parallel to the strike of the host rocks units cut by the macrofractures. These footprints are divisible into linear “core block and wing” complexes typically several hundred feet wide by 4000 to 6000 feet long. Subsequent recurrent deformation partitioned along the macrofracture surfaces imparted a “durchbewegung” texture to the contained daughter mineralization that differs markedly from the massive, coarse-grained, texture of the conformable parent bodies. Macrofractures thus further evolved into faults with net displacements measured in tens of feet up to 1 km. Two daughter orebodies exist for which no parent is known; yet its presence is mandated by the very existence of the daughters as differentiated remobilizates into metamorphic structures. Both daughter orebodies and the fault surfaces in which they occur are isoclinally refolded by the Sylvia Lake syncline, now interpreted as a major recumbent third phase fold hosting the orebodies of the district.