Chemical and isotopic data from samples of drill core and underground exposures at the volcanogenic massive sulfide (VMS) deposit at the Greens Creek mine on Admiralty Island and from VMS prospects on Woewodski Island in the Duncan Canal area about 200 km to the south indicate that both the ores and host rocks have similar compositions.These two localities are within a regional VMS belt of Late Triassic age that extends from the Windy-Craggy deposit to the northwest in British Columbia to Zarembo Island, about 20 km southeast of Woewodski Island.Although there are some felsic volcanic rocks near the Woewodski Island prospects, this VMS belt is distinguished by their absence and by the dominance of metabasalts; as well as by sparse but consistent fossil evidence for their Late Triassic age.Specifically, the major-and trace-element chemical data indicate basaltic compositions for Greens Creek stratigraphic footwall rocks and sedimentary compositions for the stratigraphic hangingwall rocks.The near-absence of bimodal volcanism and the rare-earth-element data indicate that the tectonic environment was not extensional, but are instead arc-related.The corresponding data for the Woewodski Island rocks give similar results.Although the Woewodski Island metavolcanic rocks are not as deformed or altered as those at Greens Creek, they can be confidently grouped together.

QTa Andesite and Other Intermediate Extrusive Rocks-Dark gray where fresh, green to maroon where altered; blocky weathering.Pyroxene and feldspar porphyrltic, massive to vesicular and amygdaloidal flows 10-50 cm thick.A K-Ar age of 21.2±0.6Ma was obtained from a sample in the Petersburg C-5 quadrangle and one of 21.5±0.6Ma was obtained from a sample in the Petersburg C-6 quadrangle, just west of this map area (Douglass and others, 1989, p. 63).Apparently intercalated with basalts in southern Rocky Pass area between Kuiu and Kupreanof Islands, also occurs in south central Kupreanof Island, and near exposures of "Rhyolite, Rhyodacite, etc.," (QTr) near Kah Sheets Lake, and on southwestern Zarembo Island.OFc Votcaniclastic Deposits-Unsorted and sorted pyroclastic deposits, felsic to mafic tuff, lapilii tuff, tuff breccia, and block and ash deposits.Also includes felsic to mafic lahars and oligomictic conglomerates.Deposits range from matrix-supported massive beds, 10's of meters thick, to cm-scale well-bedded turbidite-like deposits with graded beds, and thinning and fining upwards cycles.Tuffaceous deposits are generally altered to pale green clay; ashy horizons are locally silicified.Coaly plant material is rare, but present where bedding is well-developed.Mafic material subordinate to felsic material, quartz is subordinate to feldspar, and pyrite is spare but ubiquitous.Deposits lap onto volcanic centers in the vicinity of Tunehean, Lovelace, and Kushneahin Creeks on southwestern Kupreanof Island, and are intercalated with extrusive rocks at several horizons.

Nearly all of the bedrock of southeastern Alaska has been metamorphosed to some degree. Much of it has been metamorphosed under mediumto high-grade conditions during episodes that were associated with widespread plutonism. The two oldest known metamorphic episodes in southeastern Alaska occurred during an early Paleozoic and a middle Paleozoic orogeny and affected probable arc-type volcanic, sedimentary, and plutonic rocks in the area of southern Prince of Wales Island. During Late Cambrian to Early Ordovician time, rocks were penetratively deformed, flattened, and recrystallized under greenschistto amphibolite-facies conditions. The subsequent metamorphic episode, which was Silurian to earliest Devonian in age, occurred under prehnite-pumpellyite-facies conditions and was not accompanied by penetrative deformation. The predominant period of metamorphism and plutonism occurred during the interval of Early Cretaceous to early Tertiary time. The oldest documented metamorphic episode during this interval took place in northern southeastern Alaska and apparently was associated with the intrusion of elongate bodies of highly foliated, 120to 110-Ma tonalite and diorite. Low-grade metamorphism of mid-Cretaceous age produced a weakly to moderately developed metamorphic fabric in rocks extending from Kupreanof Island in the north to the peninsula north and west of Revillagigedo Island (Cleveland Peninsula) and perhaps to Revillagigedo Island in the south. This episiode predated the intrusion of mafic-ultramafic bodies that have yielded K-Ar ages of 110-100 Ma. Low-grade metamorphism of melange and flysch north of Cross Sound and on Chichagof and Baranof Islands, southwest of the Peril Strait fault, also took place sometime during the Early Cretaceous to early Tertiary interval. Metamorphism of the melange occurred in a subduction environment and may have begun a s early a s latest Jurassic time. Metamorphism during the next episode or phase was associated with the intrusion of garnetand epidote-bearing plutons of early Late Cretaceous age (approximately 90 Ma). Experimental data on the composition of magmatic garnet and the pressure required to crystallize magmatic epidote have been used to infer a minimum 13-15 kb initial depth and a 6-10 kb final depth for crystallization of the magma body. Kyanite, indicative of intermediate-pressure conditions, occurs in extenManuscript approved for publication March 26, 1987. sively developed aureoles around some of the plutons within amphibolite-facies rocks in the central and southern part of the 90-Ma metamorphic belt. Other 90-Ma plutons that intrude lowgrade rocks have narrow low-pressure aureoles. Relict andalusite that has been replaced by kyanite occurs in aureoles within amphibolite-facies rocks near the northern end of the 90-Ma belt, near northernmost Wrangell Island. The early formation of andalusite, indicative of low-pressure conditions, is hard to reconcile with the high to intermediate pressures inferred for the associated garnetand epidote-bearing plutons. The final metamorphic episode or phase was mostly synkinematic with, but may have slightly preceded, the lastest Cretaceous and early Tertiary mesozonal intrusion of a 600-km long, northwestward-trending composite body herein referred to as the great tonalite sill. The northern two-thirds of the metamorphic belt produced in Alaska during this episode is composed of an intermediate-pressure (Barrovian) sequence in which metamorphic grade increases northeastward. Isograds marking the first appearance of biotite, garnet, staurolite, kyanite, and sillimanite are generally parallel to the sill and inverted. Kyanite has not been reported in the southern part of the belt, and metamorphic pressures may not have been as high as in the north. Intermediate and felsic epizonal plutons intruded the eastern part of the belt in Eocene time during the final phase of this metamorphic episode and produced low-pressure aureoles and zones of migmatite.

Granitic plutons of Late Cretaceous to middle Tertiary age comprise three major plutonic belts that occur in a large segment of the Coast Mountains Complex east of Juneau; they can be grouped, according to petrographic and chemical characteristics, into six northwest-trending subbelts. The Admiralty-Revillagigedo belt consist of two types of plutons; those of the Grand Island subbelt consist of magnetite-free, garnetand epidote-bearing tonalites and quartz diorites, whereas the two plutons of the Taku Harbor subbelt are magnetiteand epidote-bearing, hornblende quartz monzodiorites. The two plutons of the Great tonalite sill belt are foliated, equigranular, magnetite-rich biotite-hornblende tonalites that differ from plutons from this belt to the northeast which are more acidic and felsic in composition. The Coast Mountains belt contains two major suites of plutons; the western subbelt consist of large piutonic units of predominantly massive, magnetiteand titanite-bearing biotite-hornblende granodiorite, whereas the eastern subbelt consist of undivided, massive, porphyritic, coarse-grained allanite-bearing hornblende-biotite granite and a stock of fineto medium-grained seriate granite. Across the Coast Mountains Complex, the three major plutonic belts are distinguished by abrupt changes in age, structure, mineralogy, and composition, and the six subbelts are also distinguished by abrupt rather than gradual changes in chemical and modal composition, and magnetic susceptibilities. Plutons of the Admiralty-Revillagigedo belt are characterized by high FeO*/MgO ratios, high total alkalies and iron content, and high Sr abundances (700-1000 ppm). Rocks of the Great tonalite sill belt have restricted SiC>2 range (59-66 percent), high normative An content, and high ferromagnesian trace element (Sc, Cr, Co, and Zn) abundances, whereas rocks of the Coast Mountains belt are typically more acidic (64-74 percent SiC>2), less mafic, and contain higher abundances of K^O, Rb, Ur, and Th. Granites of the eastern part of the Coast Mountains belt are further distinguished by low Sr (<400 ppm) and high Rb (>100 ppm) contents, pronounced negative Eu anomalies, and high Hf and Ta concentrations. The Wright Glacier stock is also characterized by very low Sr (<250 ppm) abundance and high Zr (280-380 ppm) and Y (30-50 ppm) concentrations. The compositional differences between rocks of the various suites or subbelts reflect their differences in age and in the lithotectonic terranes and tectonic regimes into which they were emplaced. Plutons of the Admiralty-Revillagigedo belt represent an unrelated magmatic event from the plutonism of the mainland batholithic belts. Physical and chemical features support a common origin and magmatic evolution for most plutons of the Great tonalite sill and Coast Mountains belts, but some younger granites of the eastern part of the region may have been derived from a separate and unrelated magmatic event.

QsSedimentary rocks (Quaternary) Chiefly Quaternary continental sedimentary rocks and lesser volcanic rocks, and unconsolidated silt, sand, and gravel.Depositionally overlie older overlap assemblages and terranes.Locally folded and faulted Ts Sedimentary rocks (Tertiary) Chiefly Tertiary continental sedimentary rocks and lesser volcanic rocks.Depositionally overlie older overlap assemblages and terranes.

The magnetic susceptibility of 194 granitic rock samples from along a transect of the Coast plutonic-metamorphic complex near Juneau, was measured using a Geoinstruments JH-8 model hand-held magnetic susceptibility meter.Variations in magnetic susceptibility are not only usefull in differentiating individual plutons for mapping purposes, but may aid in (1) delineating hydrothermally altered and mineralized areas, (2) determining changes in metamorphic grade, (3) interpretation of aeromagnetic data, and (4) interpreting the tectonic and petrogenetic history of pluton emplacement.The variations in magnetic susceptibility define and delineate individual plutons and plutonic units that are part of three major plutonic belts of the region.Plutons range from quartz diorite to granite in modal composition.Variations in magnetic susceptibility are due to variable abundance of magnetite in the rocks, but granitic rocks with very low magnetic susceptibility lack magnetite, but may contain ilmenite, sulfides, and secondary opaque oxides.We also experimented with a Exploranium KT-5 model susceptibility meter and found the results compatible to the JH-8 meter.Both meters can accurately measure magnetic susceptibility on slabbed hand samples of sufficient size that will duplicate outcrop values.

The entries in this bibliography span almost two centuries of the human history, scientific research, and exploration activities in the Glacier Bay region of southeastern Alaska (Fig. 1).The reports, articles, and maps listed cover a wide variety of topics, but they are all unified by one common concern.That concern is the quest for knowledge about all aspects of the region.Almost without exception, the scientists and others who have produced this material consider themselves privileged to have been part of that quest; it is their hope that this bibliography will aid in continuing and expanding comprehensive scientific studies in the region.

The Sitkoh Bay alkalic plutonic suite consists of six elongate small plutons totaling about 10 km wide by 45 km long on Chichagof Island near Tenakee Springs, southeastern Alaska. The suite, of Silurian or older age, contains a wide variety of rock types, ranging from nepheline syenite, syenite and trondhjemite to quartz monzonite and granite. This report provides majorand minor-element chemical data, including rare-earth elements (REE), for four bodies of the suite: the Kook Lake, Basket Lake, Point Hayes, and Tenakee Springs plutons. Rocks analyzed are samples typical of units mostly obtained from 1960 reconnaissance mapping. This part of Chichagof Island in the early Paleozoic was probably in or near a continental-margin volcanic arc based on the nature of country rocks of the alkalic suite, but the rocks of the suite lack fingerprints of such arc-related magmatism (for example, strong Nb depletion). The magmatism may be related to a rapid switch from subduction or collision to transcurrent tectonic activity, such as recorded for alkalic rocks from other areas. The analytical data show no evidence of significant REE or other element concentrations as are economic in other bodies of this type, but lack of mineral-resource directed sampling precludes data interpretation in terms of economic significance.

Si0 2 A1 2°3 Fe 20 3 FeO MgO CaO Na 20 Ti0 2 P2°5 MnO LOI Total Si0 2 A1 2°3 Fe 20 3 FeO MgO CaO Na 20 Ti0 2 P2°5 MnO Q C Or Ab An Ne Wo En Fs Fo Fa Mt n Ap