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Structural and tectonic analysis of the southern Peninsular, southern Wrangellia, and northern Chugach terranes, along the Trans‐Alaska Crustal Transect in the northern Chugach Mountains documents a long succession of Early Jurassic through Cenozoic deformational events. The deformational events are generally characterized by distinctive structural fabrics and metamorphisms. Most of the events are interpreted to be related to subduction‐related accretion or terrane accretion along the Border Ranges fault system (BRFS) and companion faults, and the Contact fault system (CFS). Each period of subduction‐related accretion consisted of underplating of the outboard unit beneath the adjacent inboard unit. The fabric associated with each subduction‐related accretion consisted of folding, intense shearing, and local rolling of planar structures. Age and structural relationships suggest migration of the zone of subduction‐related accretion from the BRFS to the north, through each accreting unit, to younger bounding thrust faults to the south. Other older and younger deformational events are also recognized and are interpreted to have formed before and after, respectively, accretions along the BRFS and CFS. The main younger deformational events are (1) early Tertiary north verging folding of portions of the northern Chugach and southern Wrangellia terranes and (2) broad folding and rotation of major and minor structures related to subduction‐related accretion or terrane accretion during early and middle Tertiary oroclinal bending of Alaska.

Major zinc-lead deposits occur at Drenchwater Creek in the Howard Pass quadrangle in the National Petroleum Reserve in Alaska (NPRA). Detailed geologic mapping of a 31-km 2 area shows that sphalerite, galena, pyrite, marcasite, and sparse barite occur irregularly in a zone at least 1,830 m long and 6 to 45 m wide. The sulfide deposits are in deep-water marine rocks of Mississippian age that consists of dark-gray chert and shale, tuff, tuffaceous sandstone, and sparsely distributed keratophyre and andesite flows and sills. These Mississippian rocks constitute the oldest part of the Kagvik sequence, which includes rocks of late Paleozoic and Mesozoic age. The Kagvik sequence is in the lowermost structural plate of a terrane characterized by east-west-striking gently south dipping thrust faults. The bedrock of the Drenchwater Creek area is a tectonic breccia composed of a heterogeneous mixture of lenses of different rock types; these lenses are commonly several hundred meters long by a few tens of meters wide. The sulfide minerals typically are present in hydrothermally altered chert and shale adjacent to volcanic and volcaniclastic rocks. Fragments of fine-grained feldspar, pumice lapilli, and mafic volcanic rocks in the chert and shale are commonly replaced by aggregates of kaolinite, montmorillonite, sericite, chlorite, actinolite, barite, calcite, quartz, fluorite, and prehnite. Locally the chert is altered to siliceous medium-grained metaquartzite. The sulfide minerals and barite form disseminated grains, massive sphalerite-rich layers, or, more rarely, quartz-sulfide veins that crosscut cleavage. Selected samples contain more than 1 weight percent Zn and 2 weight percent Pb, as much as 150 ppm Ag, greater than 500 ppm Cd, and as much as 500 ppm Sb and 1,500 ppm Ba. Electron microprobe analyses of sphalerite show the following atomic percentages: 44.3 to 47.5 Zn, 2.0 to 5.2 Fe, 0.3 to 0.4 Cd, and 0.1 to 0.2 Mn. Analyses of galena show the following atomic percentages: 47.8 to 49.9 Pb and 0.1 to 2.2 Sb. The pyrite and marcasite are nearly devoid of trace metals. Lead isotope analyses of galena show model lead ages of approximately 200 m.y. and indicate derivation of the lead from an average orogene, either an island-arc or Andean-type arc environment. Field and laboratory data suggest that the stratiform deposits were formed from metal-laden hydrothermal fluids discharged onto a deep-ocean floor during submarine eruptions that yielded keratophyric to andesitic flows, tuff, and sills. Later intense deformation disrupted and partly remobilized the stratiform deposits. The sulfide deposits in the Drenchwater Creek area represent a recent discovery in a region that has not been thoroughly explored. Zones of iron staining in the Kagvik sequence and zinc anomalies in stream sediments indicate favorable areas for exploration to the east and west of the Drenchwater Creek area.