Metamorphism and Polyphase Deformation of the Zinc Sulfide Orebodies of the Balmat-Edwards Mining District, NW Adirondacks, NYS. A Record of Shawinigan through Ottawan Orogenic Events In the Grenvillian Orogenic Cycle

Zinc sulfide orebodies of the Balmat-Edwards mining district, NW Adirondack Lowlands, NY State, have a fascinating history of extensive remobilization and polydeformation during the Grenville orogeny. Sphalerite dikes fractionated from conformable massive sulfide parent orebodies during high grade metamorphism and intruded macrofractures that ramp upwards across stratigraphy where the macrofractures impinge upon the parents. Coarse-grained anatectic sphalerite dikes cross-cut early-phase foliations, schistosities, and recrystallized bedding in host rock siliceous dolomitic marbles, forming elongate, sheetlike daughter orebodies within them. Distances of remobilization are 8 to 10 thousand feet or more. Discernibly later strains partitioned along macrofracture surfaces which were evolving into tectonic slides imparted finer grained durchbewegung textures to the daughter orebodies, presumably at much lower temperatures.

High temperature remobilization postdates earlier deformation of perhaps early Shawinigan age or older and may have occurred late Shawinigan. Grenvillian cooling paths for the Lowlands suggest that perhaps as much as 200 million years may have elapsed between remobilization and development of durchbewegung textures, perhaps during Ottawan time.

Shear folds of durchbewegung ore exhibit pervasive “top-side-East” asymmetric senses suggesting bulk transport consistent with Lowlands rocks having been thrust back towards the Adirondack massif, again during Ottawan time. The last major deformational phase produced the Sylvia Lake syncline, a nappe-like fold hosting the orebodies of the Balmat-Edwards district and one of several responsible for the NE-SW regional grain of the Lowlands. Tentative correlation of these folds with dated events in the BLSZ suggests a major Ottawan component of deformation in the Lowlands.