DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY

RECONNAISSANCE GEOLOGIC MAP OF CHICHAGOF ISLAND AND NORTHWESTERN BARANOF ISLAND, ALASKA By R. A. Loney, H. C. Berg, 4,J. S. Pomeroy, and D. A. Brew

MISCELLANEOUS GEOLOGIC INVESTIGATIONS MAP I-388

PUBLISHED BY THE U. S. GEOLOGICAL SURVEY WASHINGTON. D. C. 1963 DEPARTMENT OF THE INTERIOR · TO I

RECONNAISSANCE. GEOLOGIC MAP OF CHICHAGOF ISLAND AND NORTHWESTERN BARANOF ISLAND, ALASKA

By R. A. Loney, H. C. Berg, J. S. Pomeroy, anci D. A. Brew

CONTENTS The purpose of this text is to make available the information that has led the· authors to revise the Introduction ...... 1 stratigraphy of some parts ·of the map area and to Chichagof Island, Freshwater Bay area ...... 1 summarize. the stratigraphy of the remaining areas. Graywacke and argillite ...... ~ 1 The new· and revised stratigraphic units and some Kennel Creek Limestone ...... 1 newly delineated metamorphic units are treated in Cedar Cove Formation . . . ·...... 1 greater detail than the others. Detailed descriptions Freshwater Bay Formation ... ~ ...... · 1 of the structure, petrography, and other geologic Iyoukeen Formation ...... 2 features of the region, are to be published some time Eastern Chichagof Island exclusive of Fresh- in the future. water Bay area ...... 2 Argillite, graywacke, and limestone .. ·... . 2 CHICHAGOF ISLAND, FRESHWATER BAY AREA Hornfels ...... •...... ,. 2 Limestone and conglomerate ...•....· ... 2 The rocks of the Freshwater Bay area, in north­ Chichagof Island northeast of Peril Strait­ eastern Chicagof Island, have been described in detail Hoonah Sound and in vicinity of Lisianski and named by Loney, Condon, and Dutro ( 1962 ). Inlet ...... ·...... · ...... •...• 2 Summary descriptions of their units are given below. Hornfels, schist, and· marble ...... •. 2 The units form a diverse assemblage of sedimentary Western Chichagof and Baranof Islands ...... 3 and volcanic rocks of Silurian(?), Devonian, and Goon Dip Greenstone ...... 3 Mississippian age· that has a maximum cumulative Whites tripe Marble ...... ·...... 3 thickness of}Tiore than 24,000 feet. Schist ...... ; ...... · 3 Graywacke and argillite Pinnacle Peak Phyllite ...... 4 Waterfall Greenstone ...... ·... . 4 This unit, of Silurian(?) and Devonian(?) age, Kelp Bay Group ...... 4 consists· mainly of arkosic, feldspathic, and lithic Sitka Graywacke .....· ...... 5 graywacke, and argillite, with subordinate conglom­ Hornfels . . . . . • ...... ,- 5 erate, siltstone, and minor limestone. The conglom­ Edgecumbe Volcanics ...... 5 erate consists of clasts of chert, volcanic rock; Northwestern Baran of Islanci . ·...... 5 argillite, graywacke, and 'limestone in a graywacke Katlian Group ...... - ...... ,. 5 matrix. The base of the unit was not seen; about 5,000 Hornfels ...... · 6 feet of strata are exposed. Baranof Island, vicinity of Nakwasina Sound . •. 6 Kennel Creek Limestone Nakwas ina Group ...... 6 Northern Baranof Island and Chichagof Island· This formation, of Middle Devonian age, consists between Slocum Arm and Hoonah Sound . . . 6 of thin- to very thick-bedded limestone that contains Amphibolite and schist ...... • 6 sparse dolomite beds and limestone breccia. The Unconsolidated sedimentary deposits ...... 6 upper part of the formation is thin-bedded fossil­ References cited ...... 6 iferous limestone with siliceous laminae. The unit has a maximum thickness of about 5,000 feet. Cedar Cove Formation INTRODUCTION The Cedar Cove Formation, of Middle and Late(?) This map presents the results of geologic mapping Devonian age, consists of an upper limestone member during the summer. of 1961 and a compilation of the and a lower member composed mainly of thin-bedded mapping of previous workers. For background material argillite with thin limestone beds near the base, and, about the region mapped and its geological problems locally, graywacke and conglomerate. The lower part see the publications of these workers. Previous map­ of the upper member is mainly very thick-bedded ping is accepted without change except as noted in text. limestone; the ·upper part is thin-bedded and fossil­ Where an unnamed unit of previous workers is be­ iferous, and contains minor thin tuff beds. The for,;. lieved to be equivalent to one of the new map units, mation is about 2, 660 feet thick· at the type locality at the new unit name is used. The new mapping includes almost continuous traverses of the shores accessible Cedar Cove in Freshwater Bay. from small boats and foot traverses of the ridges Freshwater Bay Formation above timberline. The unconsolidated sedimentary The Freshwater Bay Formation, of Late Devonian deposits were mapped almost wholly by photogeologic age, is made up principally of andesite and basalt methods. flows, breccia, and tuff that contain minor inter- calated volcanic graywacke, limestone, and argillite. contains appreciable amounts of tremolite and probably The upper part of the formation is mostly andesite, other calc-silicate minerals, as well as streaks and the lower part mostly basalt. The formation is about disrupted layers of quartz- biotite- sodic plagioclase - 6,500 feet thick and contains brachiopods near its actinolite hornfels, which are probably metamorphosed base. argillaceous rock. Iyoukeen Formation Limestone and conglomerate The Iyoukeen Formation, of Mississippian age, This unit consists mainly of intertonguing lime­ consists of about equal parts of limestone and shale. stone and conglomerate. The conglomerate is thin The upper half of the formation consists of about and restricted areally in the eastern part of Chichagof 3,500 feet of thin- to medium-bedded limestone that Island, but thickens to the northwest at the expense of contains variable amounts of nodular to bedded chert. the limestone. The upper part of the limestone is less cherty than the lower, is locally gypsiferous, and contains abun­ Most of the limestone is medium to thick bedded dant corals; the lower part is thinner beddedand con­ and sparingly fossiliferous. Subordinate thin-bedded tains abundant brachiopods. The lower 1,500 feet of calcareous shale and siltstone and a few layers of the formation consists of grayish-black shale that conglomerate are intercalated in the lower part of contains variable amounts of limestone and shaly the section. Amphipora? sp., Favosites sp., and limestone. Abundant brachiopods, cephalopods, and Thamnopora sp. occur in thin-bedded limestone north gastropods occur in its upper part. To our knowledge of Kook Lake, and suggest a Devonian a:ge (W. A. neither the base nor the top of the formation has been Oliver, Jr., written communication, 1962 ). As a result seen. of the facies relation with the conglomerate, the thickness of the main limestone varies from probably EASTERN CHICHAGOF ISLAND EXCLUSIVE OF several thousand feet southeast of Port Frederick to FRESHWATER BAY AREA about 800 feet northwest of Port Fretlerick. The rocks that crop out in this area comprise Another limestone unit has been mapped in the three formations: an argillite, graywacke, and lime­ upper part of the formation near and northwest of stone unit that is lithologically correlative with the Port Frederick. This limestone is thin and irregularly graywacke and argillite unit of Freshwater Bay; a bedded, and contains minor shaly layers. Brachiopods occur. in the upper part and corals in the middle and limestone and conglomerate unit that is probably correlative with part or all . of the Kennel Creek basal parts of the unit. The limestone has a maximum Limestone and Cedar Cove Formation; and the Fresh­ thickness of about 2,500 feet, but is thinner or absent water Bay Formation, which is essentially the same where eroded prior to the deposition of the overlying as its counterpart in Freshwater Bay and is not volcanic rocks. discussed in this section. The conglomerate consists of clasts of volcanic rocks,· alaskite, syenite, graywacke, quartz, chert, Argillite, graywacke, and limestone and limestone in a matrix of fine conglomerate or The rocks of this unit are very similar to those graywacke. Interbedded with the conglomerate are of the graywacke and argillite unit of the Freshwater graywacke, a:rgillite, subordinate limestone breccia, Bay area, but here limestone is more abundant. The siltstone, shale, and minor amounts of limestone. limestone is thin to very thick bedded, and locally The limestone breccia, which is of limited areal forms thick lenses and thinner discontinuous layers extent, occurs in the upper part of the conglomerate; in the graywacke and argillite. The thin-bedded lime­ it consists of blocks of limestone as much as 6 feet stone commonly contains variable amounts of inter­ in greatest dimension in a matrix of graywacke or calated graywacke, argillite, and siltstone. fine conglomerate. Hornfels CHICHAGOF ISLAND NORTHEAST OF PERIL In the vicinity of intrusive bodies the rocks of ST.RAIT-HOONAH SOUND AND IN VICINITY OF the argillite, graywacke, and limestone unit have LISIANSKI INLET been metamorphosed to hornfelses. Most of the horn­ Hornfels, schist, and marble felses belong to the hornblende hornfels facies and are similar to the hornfels, schist, and marble unit This unit consists largely of intensely .folded, in the area on Chichagof Island northeast of the Peril interbedded hornfels, marble, schist, and amphibolite Strait-Hoonah Sound-Lisianski Inlet fault. At the mar­ that occur as septa and roof pendants in and bordering gins of contact metamorphic aureoles the hornfelses plutons. These rocks are probably in large part grade through incipiently recrystallized rocks, prob­ metamorphic equivalents of the rocks of Silurian(?) ably of the albite-epidote hornfels facies, into unmet­ and Devonian age at Freshwater Bay, Chichagof amorphosed sedimentary rocks. Graywackes in these Island, but correlation is uncertain. Rocks of Mesozoic outer margins are characterized by partial recrys­ age ni.ay be included in this unit along Hoonah Sound tallization of the matrix to biotite or actinolite, irreg­ and· on northwestern Chichagof Island. ular aggregates of epidote, and fine-grained inter­ The most abundant rock type is a distinctly growths of quartz and sodic feldspar, presumably layered, fine- to medium-grained hornfels in which albite or sodic oligoclase. Limestone is recrystallized hornblende dominates over biotite. The chief mineral to marble in areas of hornfels, and is commonly a assemblages, in order of their decreasing abundance, massive granoblastic calcite rock that contains dis­ are as follows: quartz - andesine - hornblende - seminated flakes of graphite. Locally, the marble 2 biotite, andesine - hornblende - biotite, andesine - could not be differentiated and are here mapped to­ hornblende, quartz - andesine -hornblende- diopside, gether as the Goon Dip Greenstone. The older of and quartz - oligoclase or andesine- biotite. In places them, the "greenstone schist" unit, may contain meta­ the hornfelses grade into more coarsely crystalline morphic rocks equivalent in part to the amphibolite granofels in which the chief mineral assemblages are: and schist unit of this report. Reed and Coats quartz - oligoclase or andesine -potassium feldspar­ assigned a Triassic(?) age to their "greenstone" biotite and (or) hornblende, garnet - oligoclase - unit because of its supposed conformity with their potassium feldspar - hornblende - diopside, calcite - overlying "limestone" and "schist" units, of possible diopside - garnet - wollastonite, and andesine - Triassic age. They-<;tssigned a "pre-Triassic(?)" age diopside. The hornblende of these rocks is generally to the underlying "greenstone schist" unit. These age bluish green (Z), and the biotite generally brownish assignments are followed here with the modification red (Z); sphene, apatite, and magnetite or ilmenite that the "pre-Triassic(?)" is more prob<;tbly Permian are common accessory minerals. Medium- to coarse­ because of lithologic similarity with rocks of known grained light-gray marble forms a conspicuous but Permian age elsewhere in southeastern Alaska. minor part of the unit. Nearly pure calcite marble is The predominant greenstone consists of dark­ common, but other mineral assemblages observed greenish-hued altered volcanic flows and sills that are as follows: calcite - diopside, calcite - talc, are commonly amygdaloidal. Interbedded with the calcite - serpentine - periclase - scapolite, and flows are lesser amounts of volcanic breccia, green­ calcite - cummin&_tonite. schist, and rarely limestone. The original minerals The hornfelses and granofelses generally show of the volcanic rocks have largely been replaced by granoblastic textures without noticeable preferred albite, epidote, chlorite, actinolite, prehnite, calcite, orientation of minerals. In places schists and amphi­ pyrite, and sphene. Rare relict crystals of labradorite bolites show a distinct planar preferred orientation and augite indicate an original basaltic composition. of mica and hornblende respectively. The amygdules commonly are composed of quartz, prehnite, epidote, and minor amounts of copper­ The above mineral assemblages indicate that the bearing sulfides (for further petrographic details rocks of the unit belong in general to the hornblende see Reed and Coats, 1941, p. 14-22). Some of the hornfels facies. Locally minor amounts of lower massive-appearing "greenstones" are penetratively grade metamorphic rocks of the albite-epidote facies foliated and are technically greenschists. Fissile albite or the greenschist facies occur, as, for example, in - chlorite - epidote greenschist is more abundant in the cataclastic zone lying along the northeast shore of the area southeast of Waterfall Lake. Peril Strait where quartz - albite - chlorite - calcite greenschist and quartz - albite - musc.ovite phyllite Whitestripe Marble occur together with metachert and cataclasites derived The name Whites tripe Marble is given to the prom­ from plutonic igneous rock. The abundance of' horn­ inent light-gray marble, averaging several hundred blende-rich rocks in the unit as a whole suggests feet in thickness, that crops out discontinuously for that they were chiefly derived from subsilicic volcanic more than 25 miles near the west coast of Chichagof rocks and sediments. The garnet-bearing quartzo­ Island. The formation· is named for its type locality, feldspathic granofels was probably derived from Whitestripe Mountain about 4}2 miles east of Portlock igneous dikes or sills of granodioritic composition. Harbor. Near Pinnacle Peak the marble is abruptly terminated by a fault, and is represented to the south­ WESTERN CHICHAGOF AND BARA.NOF ISLAND east by a few scattered thin lenses. The Whitestripe Goon Dip Greenstone is underlain by the Goon Dip Greenstone with apparent conformity; greenstone and marble are interlayered The name Goon Dip Greenstone is given to the se­ above and below the contact. The overlying Pinnacle quence of greenstone, greenschist, and marble, several Peak Phyllite is· intensely folded and foliated, and its thousand feet thick, that crops out in a belt more than contact with the marble is unclear and may be tectonic. 30 miles long in western Chichagof Island. The type The Whitestripe is here assigned a probable Triassic section crops out in the upper valley of the Goon Dip age. The marble is white to light-gray, massive, and River east of Portlock Harbor. The lower contact is generally fine-grained nearly pure calcite rock. It everywhere obscured by plutonic igneous intrusions. weathers to a medium gray, rugged surface on which The Goon Dip is overlain in the type locality by the karst topography is commonly developed (for details Whitestripe Marble; however, southeast of Pinnacle see Reed and Coats, 1941, p. 22-24). Peak the Whitestripe is represented only by a few widely separated thin lenses of marble, and the Goon Schist Dip is largely overlain by the Pinnacle Peak Phyllite. In this report the "schist" unit of Reed and Coats Although the Goon Dip Greenstone and the overlying (1941, p. 24-30), and of Rossman (1959, p. 163-166) formations are in general structurally concordant, the is assigned a Triassic(?) and Jurassic(?) age. It is nature of the upper contact is unknown because of in­ here divided in the western part of Chichagof Island tense folding, faulting, and absence of marker beds. into the following formations listed from base upward: The Goon Dip Greenstone is equivalent to the Pinnacle Peak Phyllite, Waterfall Greenstone, and "greenstone" unit of Rossman (1959, p. 157-161) in Kelp Bay Group. Reed and Coats suggested a Trias­ northwestern Chichagof Island. It is also largely sic(?) age for the "schist" unit because of fossil­ equivalent to both the "greenstone schist" and "green­ iferous limestone float of possible Triassic age stone" units mapped by Reed and Coats (1941, p. 14- which they thought might have come from limestone 22) in the Chichagof mining district. These two units in the lower part of the unit. During the present 3 mapping fossil corals suggestive of a Triassic and reddish brown. The greenstone is altered volcanic (or) Jurassic age were found in limestone in the Kelp rock in which original minerals have been largely Bay Group not far from the contact with the overlying replaced by epidote, chlorite, albite, calcite, and Sitka Graywacke of Late Jurassic and Early Cretaceous prehnite; relict crystals of plagioclase (An20-30) and age; these fossiliferous beds probably represent the augite occur sparsely. The greenstone is generally uppermost part of the "schist" unit. unfoliated, but locally it grades into greenschist with an intense cataclastic foliation. The graywacke is fine Pinnacle Peak Phyllite to medium grained and consists of subangular clasts The name Pinnacle Peak Phyllite is given to the of plagioclase (An20-30}, quartz, greenstone, and thinly laminated, siliceous phyllite of possible Triassic chert embedded in an abundant matrix composed age that crops out in a belt averaging about one mile largely of chlorite, prehnite, epidote, calcite, and wide near the west coast of Chichagof Island. The clay minerals. The radiolarian chert ranges from phyllite as mapped extends from Pinnacle Peak, the light gray to medium greenish gray and weathers type locality, southeastward for a distance of at least white; it commonly is recrystallized to very fine­ 15 miles. In the region north of Pinnacle Peak, which grained quartzite containing scattered chlorite and was not mapped during the present work, the Pinnacle albite. Peak Phyllite correlates with the basal part of the "schist" unit of Reed_ and Coats (1941, p. 24-30) and Kelp Bay Group Rossman (1959, p. 163-166), but wasnotdifferentiated The Kelp Bay Group, as mapped by Berg and by these workers. The Pinnacle p,eak is underlain Hinckley (1963) along the northwest coast of Baranof generally by the Goon Dip Greenstone and locally by Island, is here extended to southwestern Chichagof the intervening Whitestripe Marble, and overlain by Island. In northwestern Chichagof Island the Kelp Bay the Waterfall Greenstone. Because of the intense correlates with the uppermost part of the "schist" folding of the phyllite, the nature of the lower and unit of Reed and Coats(l941,p.24-30)and of Rossman upper contacts as well as the stratigraphic thickness (1959, p. 163-166). The Kelp Bay Group was tentatively is unknown. · assigned a Triassic age by Berg and Hinckley, but fossil evidence was lacking.· A scleractinian coral The phyllite is generally a dark-gray fine-grained that could be of Triassic or Jurassic age (Helen rock that contains abundant light-gray and yellowish­ Duncan, written communication, 1961) was found in gray siliceous laminae, ranging in thickness from 1 thin limestone ·on the northeast shore of Slocum Arm to 2 5 mm. The rock displays a well-developed lustrous during the present mapping. On this basis the Kelp foliation or cleavage about parallel to the siliceous Bay· Group is considered to be of Triassic or Jurassic laminae, and commonly contains abundant folds and age. lineations. The dark phyllite is composed largely of muscovite and dark graphitic dust and contains lesser The Kelp Bay Group appears to be transitional amounts of chlorite, epidote, calcite, and actinolite. with the underlying formations. In general as mapped The foliation is defined by elongate wisps of the dark here it consists of greenstone, greenschist, graywacke, dust and by the planar preferred orientation of the metachert, phyllite, and minor limestone that closely micaceous minerals. The lenticular siliceous laminae resemble lithic types in the Pinnacle Peak Phyllite consist of fine mosaics of quartz and albite around and the Waterfall Greenstone. The Kelp Bay Group is which the foliation bends. The phyllite was probably distinguished from them, however, in containing rock largely derived from thinly interbedded argillite and types characteristic of each of these two formations chert. chaotically interbedded. The same distinction holds Waterfall Greenstone for Chichagof Island south of Slocum Arm and in northwestern Baranof Island where the Kelp Bay The name Waterfall Greenstone is given to these­ Group overlies the Katlian Group, which in part is quence consisting predominantly of greenstone, but equivalent to the Pinnacle Peak Phyllite and the also containing lesser amounts of graywacke, green­ Waterfall Greenstone. The Kelp Bay Group charac­ schist, radiolarian chert, and marble, typically ex­ teristically contains a larger proportion ofgraywacke posed in the ridge lying immediately east and north of than the underlying formations, and in places seems Waterfall Lake in western Chichagof Island. The transitional with the Sitka Graywacke, but this relation Waterfall Greenstone is underlain by the Pinnacle could not be proved. Peak Phyllite; the nature of this contact is unknown because of the intense folding of the phyllite. The Cataclasites are abundant in the Kelp Bay Group. Waterfall is probably transitional both upward and These are streaked greenschist and phyllite in which laterally with the Kelp Bay Group, and appears to lenses of more resistant rock swim in a highly wedge out to the southeast near Cobol on Slocum foliated mylonitic matrix. The matrix generally con­ Arm by intertonguing with strata of the Kelp Bay sists of epidote, chlorite, muscovite, sphene, calcite, Group. In the region north of Rust Lake, not mapped and angular grains of quartz and plagioclase that during the present work, the Waterfall Greenstone grade from a few millimeters in diameter down to dark submicroscopic, mylonitic material. The resis­ was not differentiated by previous workers, and is tant lenses are most commonly radiolarian metachert included in the "schist" unit of Reed and Coats (1941, and greenstone. For further details see descriptions p. 24-30) and Rossman (1959, p. 163-166). The green­ of greenstone, graywacke, and metachert above under stone is here assigned a probable Triassic age. Waterfall Greenstone and of phyllite under Pinnacle The greenstone and graywacke are generally dark Peak Phyllite (also see· Berg and Hinckley, 1963). green and thick bedded, and characteristically weather 4 Sitka Graywacke periphery of a contact metamorphic aureole shows incipient r.ecrystallization of the matrix to biotite or park-gray, medium- to thick-bedded, medium­ actir.olite, fine-grained granoblastic aggregates of grained graywacke dominates this formation, which is epidote, quartz, and albite(?), and overgrowths of here called the Sitka Graywacke instead of Sitka Group quartz and sadie ·feldspar on detrital quartz and (Berg and Hinckley, 1963). Less abundant rock types, plagioclase fragments. in order of decreasing abundance, are thin-bedded graywacke, dark-gray argillite, conglomerate, and Edgecumbe Volcanics breccia. Minor rock types are interbedded volcanic . The Edgecumbe Volcanics consist mainly of ba­ rock and chert, and interbedded greenschist, slate salt flows of tholeiitic affinities extruded from Mt. and limestone. Fossils, including several species of Eclgecumbe and nearby vents. Deposits of ash, lapilli, Buchia indicative of Late Jurassic and Early Creta­ and, rarely, tuff-breccia are associated with the flows. ceous age (D. L. Jones, written communication, 1962), The basalt is porphyroaphanitic to aphanitic with large occur in argillite and graywacke at several localities phenocrysts and scoriaceous flow tops characterizing along the southwest shore of Slocum Arm and the th(:! dominant rock type; less common is massive non­ formation is assigned this age. Inoceramus prisms vesicular lava with small phenocrysts or none at all. indicative of a prob11ble Jurassic or Cretaceous age The different flows vary in thickness from 0. 5 to sev­ (D. L. Jones, written communication, 1961) were eral meters, and most are columnar jointed and contain found in calcareous slate interbedded with pillow lava, small domes. Most of the .flows are dark gray and con­ argillite, greenstone, and limestone on the southwest trast with the yellow and reddish-orange ash and side of Emmons Island in Hoonah Sound; 'these beds lapilli that mantle the upper slopes ofMt. Edgecumbe. probably correlate with the Sitka Graywacke. Berg and Hinckley (1963) consider the volcanics to Feldspathic graywacke is the most abundant type be quaternary in age. · of graywacke, followed, in order of decreasing abun­ The olivine content of the basalt ranges from 0 to dance, by lithic and arkosic graywacke. The detrital 15 percent with most of the olivine occurring as anhe­ grains are angular to subrounded and range in size dral phenocrysts a maximum of 3 mm in diameter. from very fine sand to very coarse sand. The princi­ Many of the phenocrysts are rimmed by pyroxene. pal grain constituents are as follows: quartz, undula­ Scattered fine grain of olivine also occur in the inter­ tory, 5-30 percent; plagioclase (An27 -37 ), 10-30 per­ granular mesostasis. Plagioclase phenocrysts cent; lithic fragments, composed mostly of argillite, (Anso-87) constitut·e 40-50 percent of the basalt. Pla­ greenstone, and chert, 10-40 percent; potassium feld­ gioclase laths in the mesostasis have the composition spar 0-15 percent. The matrix forms on the average An:38-56· Subhedral pyroxene phenocrysts make up 15- about 40 percent of the rock, and consists mainly of 20 percent of the basalt; augite is most common, fol­ chlorite, very fine aggregates of authigenic quartz lowed by hypersthene and enstatite. As much as and albite, sericite, clay minerals, and fine detritus. one-half of the pyroxene in some of the olivine-poor For further petrographic descriptions see Reed and basalt is pigeonite .. Dark brown, partly devitrified Coats (1941, p. 33-35), and Rossman (1959', p. 167). glass forms 15-20 percent of the rocks and magnetite Hornfels and secondary products make up about 10 percent. Where the Sitka Graywacke has been intruded by NORTHWESTERN BARANOF ISLAND granitic rocks, it has been converted to hornfels of the hornblende-hornfels facies. The hornfelses are Katlian Group generally fine grained and porphyroblastic or grana­ The name Katlian Group is here given to the low­ blastic in texture; some of the rocks interbedded with grade metamorphic rocks that crop out in northwestern typical hornfels show marked planar preferred orien­ Baranof Island and correlate with rocks to the north on tation of micas, but this foliation is probably mimetic. southwestern Chichagof Island. The type locality is Mt. The hornfels ordinarily consists of plagioclase Katlian, about 9 miles northeast of Sitka. The Katlian (An25-40), quartz, and reddish-brown (Z) biotite or Group comprises the more deformed lithic equivalents pale-green (Z ) hornblende, with subordinate amounts of the Goon Dip Greenstone, Whitestripe Marble, Pin­ of potassium feldspar and muscovite, and accessory nacle Peak Phyllite, and Waterfall Greenstone, and is sphene, apatite, zircon, graphite, tourmaline, pyrite, therefore considered to be probably Permian and Tri­ and magnetite or ilmenite. Locally, the hornfels con­ assic in age. To our knowledge, the lower contact of tains as much as 20 percent of cordierite, and in a the Katlian Group has not ·been seen; the upper contact few places as much as 10 percent of pink garnet. with the Kelp Bay Group, although complicated by de­ Andalusite · and sillimanite have been reported in formation, appears to be transitional. In general the hornfels of the Sitka Graywacke on northwestern Katlian Group is distinguished from its lateral equiv­ Chichagof Island. Contact metamorphism of calcareous alents listed above and from the Kelp Bay Group by the rocks in the Sitka Graywacke has produced hornfelses presence of an intense, pervasive foliation that has dis­ consisting mainly of diopside, quartz, and plagioclase, rupted bedding and has prevented further subdivision of with subordinate calcite, sphene, and pyrite. the group. In the outer margins of contact metamorphic The Katlian Group is composed of intensely foli­ aureoles, these hornfelses grade through partly re­ ated fine-grained cataclastic phyllite, greenschist, and crystallized rocks that are probably in the albite­ semischist through which are scattered sheared lens­ epidote hornfels facies into rocks that show only the es, ranging in length from a few inches to several tens effects of diagenesis. Typically, graywacke from the of feet, composed of thinly interbedded white-weather- 5 ing, radiolarian metachert and reddish-brown-weath­ quartzofeldspathic schist, and minor amounts ofmar­ ering greenstone. Similar lenses of massive, reddish­ ble that crop out in the vicinity of the west arm of brown-weathering greenstone are also common. Both Peril Strait. It also includes lesser amounts of types of lenses closely resemble the rock types char­ cataclasite and hornfels in the area between Hoonah acteristic of the Waterfall ,Greenstone. The phyllite and Sound and Slocum Arm. In general these rocks are greenschist commonly contain abundant elongate augen probably high-grade metamorphic equivalents of the of very fine-grained quartzite, which has been derived greenstone, graywacke, phyllite, and marble of prob­ largely from radiolarian chert. The augen lie in a dark­ able Mesozoic age that crop out along strike in the gray foliated mylonitic matrix composed of newly above area, but may include late Paleozoic rocks. formed albite, muscovite, chlorite, epidote, prehnite, The Paleozoic(?) "marble-gneiss" sequence of Ross­ biotite, and angular relict grains of quartz and plagio­ man (1959, p. 149-156) mapped west of Lisianski clase, which grade down in size to submicroscopic Inlet is on strike with this unit and may be equivalent. mylonitic dust. The phyllite grades into greenschist by The chief rock types of the unit, in order of an increase in chlorite and a decrease in muscovite. decreasing abundance, are as follows: quartz - ande­ These rocks of the Katlian Group resemble closely sine - hornblende - biotite amphibolite, andesine - those of the Pinnacle Peak Phyllite. Graywacke, semi­ · hornblende amphibolite, and quartz - oligoclase or schist, and serpentine are minor constituents of the andesine - potassium feldspar - biotite - garnet Katlian Group. schist. The amount of quartz and feldspar in these Hornfels rocks varies considerably giving them a striking banded appearance caused by the alternation of light North of Katlian Bay, near a gabbroic plutonic quartzofeldspathic and dark mafic layers. The rocks body, the rocks of the Katlian Group have been meta­ are characterized by a pronounced foliation defined by morphosed to medium-grained, thinly layered quartz­ the planar preferred orientation of micaceous and andesine - hornblende - biotite hornfels. Mineralogi­ prismatic minerals. Marble is a minor but prominent cally, these rocks are typical of the hornblende horn­ constituent of the unit; it is nearly pure calcite, but fels metamorphic facies, and the layered, g:ranoblastic commonly contains small amounts ofdiopside, brucite, textures suggest the superposition of contact metamor­ and calcic plagioclase (An86-9Q). The hornblende of phism on previously foliated rocks. The hornfels 1typ­ the above assemblages is bluish green (Z), and the ically consists of alternating layers of dark-greenish­ biotite is reddish brown (Z). The association horn­ gray hornblende-rich and light-gray quartzofeldspath­ blende - plagioclase (=--AnlQ) and the presence of ic rock, which average about 1 em in thickness. The garnet tn both amphibolites and pelitic schists suggests mineral constituents of the most abundant hornfels are the almandine amphibolite facies. as follows: 50 percent plagioclase (An28-47), 20 per­ cent hornblende (Z= deep green), 20 percent undula­ Locally, cataclastic deformation has produced tory quartz, 8 percent biotite (Z= dark brown), and 12 zones of lower grade phyllite and schist in which the percent accessory potassium feldspar, sphene, apatite, assemblage quartz - albite - muscovite - chlorite in­ zircon, magnetite or ilmenite, pyrite, garnet, and dicates the greenschist facies. Northwest of the west muscovite. Common products of retrogressive meta­ arm of Peril Strait the amphibolite and schist become morphism are epidote (after hornblende), chlorite finer grained, but no accompanying decrease in meta­ (after biotite), and sericite and kaolinite (both after morphic grade was observed. A belt of cataclasites feldspar). The hornfels is cut by veinlets of prehnite, was mapped with this unit along the South Arm of albite, and quartz. Hoonah Sound. In places the cataclasites have been crystallized, possibly by contact metamorphism, to BARANOF ISLAND, VICINITY OF both albite - chlorite and oligoclase - or andesine - NAKW ASINA SOUND hornblende hornfels; some of the cataclasites have been derived from plutonic igneous rocks. Nakwasina Group The Nakwasina Group of Berg and-Hinckley·( 1963) UNCONSOLIDATED SE_DIMENTAR Y DEPOSITS on the northwest coast of Baranof Island is mostly Unconsolidated sedimentary deposits of Quater­ lithically equivalent to the Katlian Group, and partly nary age occur in lowlands throughout the map area. equivalent to the Kelp Bay Group. The Nakwasina Included in the map unit are alluvium, colluvium, gla­ is composed largely of metachert, volcanic rocks, and cial till and outwash, and ash and lapilli ·from the greenstone; marble, graywacke, argillite, phyllite, eruptions of Mt. Edgecumbe volcano. calcareous siltstone, schist, and hornfels occur local­ ly. Berg and Hinckley (1963) considered the Nak­ REFERENCES CITED wasina Group to be Paleozoic(?) in age; in this repo"rt it is considered to be Permian(?) and Triassic(?) in Berg, H. C., and Hinckley, D. W., 1963, Reconnais­ age. sance geology of northern Baranoflsland, Alaska: U.S. Geol. Survey Bull. 1141-0. NORTHERN BARANOF ISLAND AND CHICHAGOF Lathram, E. H., Loney, R. A., Condon, W. H., and . ISLAND BETWEEN SLOCUM ARM AND Berg, H. C., 1959, Progress map of the geology HOONAH SOUND of the Juneau quadrangle, Alaska: U.S. Geol. Survey Misc. Geol. Inv. Map I-303. Amphibolite and s'chist Loney, R. L., Condon, W. H., and Dutro, J. T., Jr., This unit largely includes the intensely folded, 1962, Geology of the Freshwater Bay area, interbedded, medium- to coarse-grained amphibolite, Chichagof Island, Alaska: U.S. Geol. Survey Bull. 1108-C. 6 Reed, J. C., and Coats, R. R., 1941, Geology and ore Rossman, D. L., 1959, Geology and ore deposits of deposits of the Chichagof mining district, Alaska: northwestern Chichagof Island, Alaska: U.S. Geol. U.S. Geol. Survey Bull. 929, 148 p. Survey Bull. 1058-E, p. 139-216.

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