Magmatic-Hydrothermal Systems and Epithermal-Style Mineralization in Western Pacific
Arc Environments: Conical Seamount and Desmos Caldera, Papua Nuew Guinea
Peter M. Herzig
Freiberg University of Mining and Technology, Germany
E-mail: herzig@mineral.tu-freiberg.de
Mark D. Hannington (Geological Survey of Canada),
Ray A. Binns (CSIRO Exploration and Mining, Australia),
Toshitaka Gamo (Ocean Research Institute, Japan)
ODP drilling has previously focussed only on seawater-dominated hydrothermal systems
with associated massive sulfide mineralization (Middle Valley, TAG, Pacmanus). However,
black smoker hydrothermal systems on the mid-ocean ridges and in deep back-arc basins
represent only one type of seafloor hydrothermal activity. We propose to explore for the first
time the subsurface nature of two contrasting magmatic-hydrothermal systems by drilling at
Conical Seamount (New Ireland Fore-Arc) and Desmos Caldera (Manus Back-Arc), Papua New
Guinea. The style of alteration and mineralization in surface samples from Conical Seamount
and Desmos Caldera, including extremely high concentrations of gold at Conical Seamount (up
to 230 ppm Au), indicates a similarity to subduction-related epithermal systems and gold
deposits on land rather than to conventional black smoker-type seawater circulation systems.
Drilling at Conical Seamount and Desmos Caldera will provide important information on the 3rd
dimension of this newly discovered type of seafloor hydrothermal system which will have
considerable implications for our understanding of seafloor and land-based mineral deposits.
The proposed drilling also provides a unique opportunity to link the results of Leg 192
and 193 to the larger history of the Pacific-Australian plate margin, and at the same time help to
characterize a new type of fossil seafloor hydrothermal system.
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Scientific objectives
Drilling magmatic-hydrothermal (i.e., epithermal) systems at a fore-arc volcano (Conical
Seamount: New Ireland Fore-Arc) and in a back-arc environment (Desmos Caldera: Manus
Back-Arc) will contribute to the overall scientific objectives of the Ocean Drilling Program Long
Range Plan (1996).
Hydrothermal Processes and Gold Mineralization
To date, only seawater-dominated hydrothermal systems have been drilled by the Ocean
Drilling Program (Leg 139: Middle Valley, Leg 158: TAG, Leg 169: Middle Valley/Escanaba
Trough, Leg 193: Manus Basin 2000/01). Drilling of epithermal systems, for which a
contribution of reactive magmatic fluids and gases has been documented, is the logical
continuation of the ODP efforts to understand fluid circulation and magmatic processes in the
oceanic crust. Drilling in these systems will provide the first subseafloor samples and the first
quantitative measurements of the magmatic heat and material fluxes associated with
submarine epithermal systems. The proposed drilling will provide new data on the formation,
the tectonic and magmatic controls, as well as the alteration and (gold) mineralization
associated with epithermal systems in both a volcanic fore-arc and back-arc environment.
The comparison of an inactive low-sulfidation epithermal system (Conical Seamount) with an
active high-sulfidation system (Desmos Caldera) will also provide new insights into the
formation of mineral deposits in subduction-related tectonic environments. This is of
considerable importance, as many of the giant gold deposits on land are thought to have
formed in similar geological settings.
Mass Balance and Temporal Variability at Subduction Zones
The proposed drill sites include two different volcanic environments both related to the
same subduction regime Conical Seamount is an alkaline volcano in a rifted fore-arc setting
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of the New Ireland Basin. Desmos is a calc-alkaline volcano typical of extensional
environments in back-arc basins. The present crustal thinning in the New Ireland Basin is
thought to be related to extension in the Eastern Manus Basin, opposite New Ireland, where
the Desmos Caldera has formed. The complexity of this setting, including the possible
involvement of both the Solomon and Pacific Plates (i.e., subduction reversal), is considered
to be a key factor in the genesis of giant gold deposits. A comparison of the magmatic history
and the possible links between these two settings will contribute to an improved
understanding of material fluxes and interactions in complex subduction zone environments.
Role of Magmatic Volatiles in Biogeochemical Processes
Magmatic volatiles are important contributors to the ocean's chemistry and - based on
land experience - are an important source of energy for distinct microbiological communities.
Most of the present knowledge about biological and geological interactions in seafloor
hydrothermal systems is based on the paradigm of seawater-basalt reaction as the sole source
of chemical nutrients. The role of magmatic volatiles in microbial chemosynthesis is an
important subject which so far has not been addressed by ODP. Drilling seafloor magmatic-
hydrothermal systems is the only way to provide new insights into this high-priority research
area.
Both target areas are uniquely characterized by hydrothermal systems with unequivocal
evidence for the presence of magmatic volatiles. This has resulted in the formation of both
high-sulfidation epithermal-style mineralization with intense acid alteration (Desmos) and
low-sulfidation epithermal mineralization with extreme enrichments in precious metals
(Conical Seamount). The origins of these fluids (e.g., volatiles derived from magmas
associated with subduction-modified crust) and their importance in subduction zone volcanic
enrironments remain poorly understood. Drilling at Conical Seamount and Desmos will
provide the first opportunity to quantify the role of magmatic contributions in seafloor
hydrothermal systems in two key volcano-tectonic settings. Establishing the 3-D structure
and extent of water-rock interactions at these sites will also provide the first data on material
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fluxes associated with submarine magmatic-hydrothermal activity. The largely unknown role
of magmatic volatiles in submarine biogeochemical cycles will be examined, and the potential
for microbial activity in a unique geochemical environment in the deep interior of the
volcanoes will be tested.
The main scientific objectives for drilling at both sites are:
1) To determine the structure, size, mineralogy and geochemistry of sub-seafloor epithermal-
style alteration and (gold) mineralization. How the vein mineralization develops with
depth or whether massive sulfides might be present in the subseafloor is presently
unknown.
2) To investigate the chemical interactions associated with submarine magmatic-hydrothermal
systems (including biogeochemical interactions). How magmatic volatiles influence the
geochemical characteristics of the hydrothermal fluids and the associated alteration and
mineralization in a submarine environment is poorly understood.
3) To sample the root zone of epithermal systems proximal to the magmatic source in order to
quantify the magmatic contribution of reactive gases and trace elements, to determine if
submarine epithermal-style deposits might be associated with porphyries at depth, as is
often the case on land, and to test the hypothesis that the high gold grades are related to a
magmatic input.
4) To compare the geological and geochemical characteristics of these systems with their
better-known subaerial analogs, including the nearby world-class Ladolam gold deposit on
Lihir Island.
5) To compare the results from Conical and Desmos with other drilled sites of seafloor
mineralization (seawater-dominated hydrothermal systems such as Middle Valley, TAG,
and Pacmanus) and to broaden the spectrum of known types of modern seafloor
hydrothermal systems.
To address these objectives, it is essential to obtain information from the deeper parts of
the systems, in particular where the magmatic volatiles equilibrate with the wall rocks. High-
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sulfidation conditions in subaerial systems arise when magmatic volatile mix directly with
convecting meteoric water. Leaching of the wall rock generally occurs within the zone of ore
formation, leaving vuggy quartz which may be infilled by sulfosalts, enargite, luzonite and
tennantite (Hedenquist et al., 1996). Zoned alteration surrounding the ore zones reflects the
highly acid nature of the ore fluids and comprises mainly advanced argillic assemblages that
grade outward from kaolinite-alunite to illite smectite. In low-sulfidation systems, the
magmatic volatiles are neutralized by interaction with the volcanic rocks and mixing with
deep circulating meteoric water below the ore zones. The resulting near-neutral, reduced
fluids precipitate base metal sulfides (e.g., pyrite, Fe-rich sphalerite, arsenopyrite) as a result
of conductive cooling or further mixing with near-surface waters. Characteristic alteration
assemblages associated with low-sulfidation deposits consist of smectite-illite±K-feldpar and
calcite near the site of ore deposition grading outward into chlorite (Hedenquist et al., 1996).
Mixing with seawater, which has a much higher buffer capacity than meteoric water, may
result in enhanced sulfide precipitation at depth. However, such interactions have not yet
been described from fossil deposits or from active submarine magmatic-hydrothermal
systems. Careful documentation of the alteration and mineralization through drilling will
permit reconstruction of fluid, rock, and mineral interactions in both systems and provide
criteria for the recognition of similar mineralizing environments in the geologic record.
Drilling both sites will allow a comparison of high- and low-sulfidation epithermal systems
and provide detailed information on structural, geochemical and geophysical parameters
which control the formation of epithermal deposits in the marine environment.
Epithermal deposits are often associated with deep Cu-rich ores which form from
magmatic brines in proximity to the subvolcanic magma chamber. This so-called porphyry
Cu-style mineralization is derived from Cl-rich brines that are separated from a magmatic
vapour rich in CO2, H2S, SO2 and trace metals (Hedenquist and Lowenstern, 1994).
Porphyry Cu deposits are often considered to be the root zones of highly telescoped
mineralizing systems in which the magmatic brines contribute to a variety of different styles
of mineralization from deep Cu-rich stockworks to near-surface hot spring-type gold deposits.
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A close spatial relationship has been documented between epithermal-style gold
mineralization and underlying porphyry systems in many deposits (e.g., Ladolam gold deposit
at Lihir: Müller and Groves, 2000). The recognition that certain types of fossil porphyry Cu-
Au deposits have formed in a submarine environment (e.g. Sillitoe et al., 1983, 1994) raises
the possibility that submarine epithermal systems at Conical and Desmos might be genetically
linked to subseafloor porphyries. Drilling may provide the opportunity to further test this
model. At Desmos, analysis of the venting hydrothermal fluids shows the direct input of
magmatic volatiles, implying that the active vents may be proximal to the magmatic source
(e.g. Sillitoe et al., 1996). This site may thus provide the best opportunity to drill the root
zone of an active magmatic-hydrothermal system.
Background: Conical Seamount
Conical Seamount was discovered during cruise SO-94 of R/V Sonne (Germany) and
revisited during cruise SO-133 in 1998 (Herzig et al., 1994; Herzig and Becker, 1996). It is
located in a zone of recent seismic and volcanic activity and elevated heat flow only 10 km south
of Lihir Island, which is host to the giant (40 million ounces) Ladolam epithermal gold deposit
(Moyle et al., 1990). The island of Lihir is part of the Tabar-Lihir-Tanga-Feni island chain,
which is situated in a fore-arc basin behind the presently inactive Manus-Kilinailau trench
northeast of Papua New Guinea. Alkaline volcanic activity on the islands, which began about
3.5 Ma ago, appears to be controlled by extension along northeast-trending structures that cut
across the New Ireland Basin (McInnes and Cameron, 1994). These structures are though to be
related to regional plate rotation and the opening of the Manus Basin on the opposite side of New
Ireland.
Bathymetric mapping during cruises SO-94 and SO-133 documented that Conical
Seamount has a basal diameter of about 2.5 km and raises about 600 m above the surrounding
seafloor at 1.700 m water depth. A summit plateau (150 x 200 m) made up of slightly
sedimented ankaramitic basalts and trachybasalts occurs at 1.050 m water depth. Comprehensive
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TV-grab sampling at the summit of Conical Seamount recovered distinctive epithermal-style
polymetallic vein mineralization and pyritic stockwork material with local intense clay-silica and
alunite alteration. Maximum gold grades in this material reach 230 ppm Au (avg. 25 ppm Au,
n=40). This style of alteration and mineralization is typical of epithermal gold deposits on land
which have not previously been recognized at the modern seafloor. Epithermal deposits are
commonly characterized by the presence of magmatic fluids which are responsible for
widespread gold mineralization and distinctive alteration. The presence of alunite and the
occurrence of sulfides, both showing magmatic sulfur isotope ratios, and the vein-style type of
mineralization strongly indicate the role of magmatic fluids and gases in the hydrothermal
regime at Conical Seamount (Herzig and Hannington, 1995; Herzig et al., 1999). This is in
contrast to conventional polymetallic massive sulfide mineralization largely formed by
hydrothermal convection of seawater through the oceanic crust.
The present mapping and sampling of Conical Seamount suggest that the interior of the
volcano may be mineralized similar to the nearby world-class Ladolam gold deposit in the Luise
Caldera on Lihir Island. Drilling at the summit area is therefore required to determine the extent
and character of mineralization at depth. ODP drilling at Conical Seamount would be the first
opportunity to explore the third dimension of a shallow-marine epithermal system at the modern
seafloor. This is a logical continuation of previous ODP efforts which have focussed on drilling
seawater-dominated hydrothermal systems at mid-ocean ridges and in back-arc basins.
The proposal is for a series of holes in young arc crust in the New Ireland Basin. Active
extenstion in the Manus Basin - the target area for Leg 193 - is believed to be responsible for
thinning of the old forearc crust of New Ireland and has led to recent volcanism along
extensional faults within the Lihir Island Group. Docking of the Ongtong Java Plateau - the
focus of Leg 192 - also has played a major role in establishing the present tectonic framework of
the New Ireland convergent margin. The proposed area of drilling is of interest because of new
evidence for the generation of high-K calcalkaline to shoshonitic arc magams as a result of
partial melting of metasomatismed mantle (hydration caused by dewatering of the subducted slab
at the edge of the Ongtong Java Plateau). The proposed site is also of interest because of the
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recent discovery of a large vein-style gold system on one of the young submarine volcanoes.
The gold deposit found on Conical Seamount is the first of its kind on the modern seafloor and it
bears a striking resemblance to nearby gold deposits on the island of Lihir. Evidence from
detailed petrologic and isotopic studies suggest that the gold mineralization is a direct
consequence of large-scale metal recycling in the mantle.
Geological Setting
In 1994 and 1998, the German RV Sonne conducted detailed mapping in a seismically
and volcanically active zone with elevated heat flow south of Lihir Island, Papua New
Guinea. The 1998 cruise was a follow-up of reconnaissance surveying in 1994, which
originally mapped the areas surrounding the Tabar-Lihir-Tanga-Feni island chain (TLTF) to
the east of New Ireland. A number of previously unknown seamounts between Lihir Island
and the New Ireland arc were discovered (Herzig et al., 1994; Herzig and Hannington, 1995;
Herzig et al., 1999).
The New Ireland Basin of Papua New Guinea occupies a fore-arc position with respect to
the former Manus-Kilinailau arc-trench system and hosts a series of Pliocene to Recent
alkaline volcanoes built on rifted Miocene sedimentary basement. The island of Lihir is part
of the Tabar-Lihir-Tanga-Feni island chain, situated on the old fore-arc crust behind the
presently inactive Manus-Kilinailau trench (Fig. 1).
Westward subduction along the Manus-Kilinailau trench was blocked at 24-11 Ma by the
collision of the Ontong Java plateau (Coleman and Kroenke, 1981). The resulting plate
rotation and stress relocation caused a subduction reversal from S-SW to N-NE and the
formation of the presently active north-northeast-facing New Britain Trench. The southward
migration of New Britain in the late Miocene along a series of faults isolated New Ireland and
probably also the early Tabar-Feni island chain from subduction zone processes. At that time
calc-alkaline volcanism ceased on New Ireland. The volcanic activity on the islands, which
began about 3.5 Ma ago, appears to be related to extension along northeast-trending structures
that cut across the New Ireland Basin (Stewart and Sandy, 1988; McInnes and Cameron,
8
1994). These structures are thought to be related to regional plate rotation and the opening of
the Manus Basin on the opposite side of New Ireland. Since Pliocene-Pleistocene time,
partial melts associated with extension in the thickened crust of the New Ireland Basin have
risen through the old fore-arc crust along reactivated faults to form the present volcanic
islands of the Tabar-Feni chain. The Lihir island group itself is situated on a large uplifted
block, raised by regional southward compression along the Manus-Kilinailau trench.
Records of seismic activity between the Lihir group and New Ireland show that shallow
earthquake epicenters are confined to a distinctive NE-SW corridor along the axis of the Lihir
group (Port Moresby Geophysical Observatory, 1994). The earthquakes define a narrow
seismic zone, and the recent tectonic activity along this corridor may be an indication of the
beginning of the break up of New Ireland in response to the present subduction of the
Solomon Plate and back-arc spreading in the Manus Basin. New Ireland is already notably
thinned along the portion of the island immediately opposite Lihir.
The few radiometric dates available indicate that the most recent volcanic eruptions on
Lihir occurred at about 1.1 Ma (Johnson et al., 1976). The most recent eruption in the island
chain was dated at 2300 years ago at Feni (Licence et al., 1987). The discovery of even
younger volcanic cones in the area south of Lihir implies that volcanism in the New Ireland
Basin is now focussed in the active tectonic zone of the Lihir group.
Petrology
The volcanic rocks of the Tabar-Feni chain belong to the high-K, SiO2-undersaturated
magma series and include basanite, alkali-olivine basalt, olivine nephelinite, tephrite,
ankaramite, trachybasalt, trachyandesite, tephritic phonolite, and phonolitic trachyte that have
formed in a tensional tectonic environment (Wallace et al., 1983; Kennedy et al., 1990a,
1990b; McInnes 1992; McInnes and Cameron, 1994; Patterson et al., 1997). These rocks are
unique among the islands of the Bismarck Archipelago and are consistent with a model which
involves local extension in an area of regional convergence and compression. The unusually
9
high content of volatiles and alkalis in these lavas seem to indicate a large slab-derived
component in the magmas (Kennedy et al., 1990b; Patterson et al., 1997).
Conical Seamount, the largest of the seamounts south of Lihir, rises more than 600 m
above the surrounding seafloor to a depth of 1050 m. This volcano appears to be built of
massive basaltic flows and pillow lavas. Although the flanks of the volcano are sedimented,
its symmetrical shape and dramatic relief suggest that the cone is youthful. The rocks
recovered from Conical Seamount consist of relatively fresh, vesicular, high-K calc-alkaline
to shoshonitic pyroxene-phyric basalt (ankaramites) with abundant phenocrysts of
clinopyroxene (diopside), magnetite, rare olivine and biotite. Plagioclase and magnetite are
common in the matrix and occur as small phenocrysts. Chemical analyses indicate that the
submarine lavas are similar to the subaerial portions of the TLTF island chain (Herzig et al.,
1994; Stracke, 1996; Farr et al., 1999), however, they do not show the same compositional
range as those from the islands. Enrichments in large ion lithophile elements (LILE) coupled
with relatively low high-field strength element (HFSE) abundances and moderate light-rare
earth element enrichments confirm their arc-like affinities (e.g. Farr et al., 1999). The
chemical characteristics of the volcanics are consistent with a model that involves melting of
depleted mantle that has been variably enriched via at least two subduction events (McInnes et
al., 1999).
Hydrothermal Mineralization and Alteration
Gold-rich polymetallic sulfide veins and associated pyrite stockwork mineralization have
been recovered from the top of Conical Seamount. Samples from the summit plateau of
Conical Seamount contain up to 230 ppm Au (avg. 26 ppm, n=40) with high concentrations of
Ag, As, Sb, and. The mineralization is largely fine-grained and consists of native gold and
electrum together with sphalerite, galena, pyrite, chalcopyrite, marcasite, various sulfosalts.
Late-stage As-Sb mineralization includes stibnite, realgar, orpiment, and a variety of non-
stochiometric collomorphic Fe±Pb±As±Sb-sulfides. Intense illite-smectite-amorphous silica
alteration, with local chlorite and minor adular-sericite, has affected large parts of the summit
10
area. The intense clay-silica alteration at the top of Conical Seamount grades outward into
weakly altered basalt breccias. Camera surveys across several hundred meters of the top of
Conical Seamount revealed widespread but discontinuous patches of staining caused by low-
temperature, diffuse hydrothermal vents that were formerly active near the summit of the
volcano. Visible alteration is exposed over a strike length of at least 250 m, and dredging of
the flanks of the volcano also recovered intensely altered lavas with weak mineralization.
Abundant Fe-oxide gossan implies that the hydrothermal system is now extinct.
Mineralization at Conical Seamount has geochemical and mineralogical characteristics
typical of both, auriferous VMS and epithermal gold deposits. The main stage of gold
mineralization appears to be associated with low-sulfidation, near neutral fluids and adularia-
sericite alteration that overprints earlier high-sulfidation pyrite-alunite mineralization and
alteration. This constitutes a new type of mineralization not previously recognized on the
modern seafloor. Land-based analogs typically have larger vertical dimensions, with vein
systems tapping deep geothermal reservoirs. The present mapping and sampling suggests that
the entire upper part of Conical Seamount may be mineralized at depth, however, the
difficulty of sampling prevents a proper assessment of the 3rd dimension. Drilling of the
summit area is required to determine the extent and character of mineralization and fluid-rock
interaction at depth.
Mineralization at Conical Seamount shows geological, geochemical, and mineralogical
characteristics that are transitional between conventional seafloor sulfide and epithermal gold
deposits found on land. The proximity of Conical Seamount to the presently active hot spring
environment of the giant Ladolam gold deposit on Lihir Island further suggests that both
submarine and subaerial epithermal mineralization may be linked to the same district-scale
magmatic events. Detailed comparisons of the petrogenesis of Conical Seamount and the
underlying crust with that of the Lihir volcano will help to constrain the larger-scale tectonic
history of the area.
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Background: Desmos Caldera
The Desmos Caldera is located in the eastern Manus Basin, opposite New Ireland (Fig.
1). This part of the Manus Basin is dominated by two en-echelon volcanic ridges within a zone
of regional stretching with little or no spreading (Binns and Scott, 1993; Gamo et al., 1997).
Present-day submarine volcanic activity (basalt to rhyolite) is related to thinning of the Eocene-
Oligocene arc crust as a result of extension caused by northward subduction of the Solomon
Plate at the New Britain Trench (Binns et al., 1995).
Desmos is a mafic volcano located within a 60 km-wide extensional zone of the
Southeastern Ridge (SER) (Binns and Scott, 1993; Gemmell et al., 1999, Fig. 1). The volcano is
characterized by a 250 m deep, 1.5 x 2.0 km summit caldera slightly elongated in a northwesterly
direction. Unaltered lavas within the caldera are vitreous to basaltic andesites with occasional
microphenocrysts of calcic plagioclase, augite and rare olivine. A small but very active
hydrothermal field, called Onsen, was discovered on the northern wall of the caldera at 1.930 m
depth (Gamo et al., 1997, Fig. 3). Extensive silicic and advanced argillic alteration of the
basaltic rocks as well as disseminated pyrite is associated with hydrothermal venting but no
massive sulfides have been observed (Gemmel et al., 1999). The advanced argillic (epithermal-
style) alteration assemblage consists of quartz, kaolinite-dickite, native sulfur, alunite, diaspore,
pyrophyllite and pyrite. The δ34S-values of native sulfer are among the lightest yet reported
from the modern seafloor (+5.9 ‰ to -6.8 ‰ δ34S; Gemmel et al., 1999) and indicate a unique
34S-depleted source of magmatic origin. The δD and δH2S of the vent fluids, as well a the δ
18O of the altered basaltic rocks, inidicate a significant magmatic component to the
hydrothermal sytem (Gamo et al., 1997; Gemmell et al., 1999). The alteration assemblage at
Desmos is interpreted to be a product of highly oxidized, acid-sulfate fluids. The extreme acid
leaching and distinctive aluminous alteration are typical of subaerial high-sulfidation
environments and are caused by introduction of volcanic SO2 and HCl as magmatic volatiles
(Hedenquist and Lowenstern, 1994; White and Hedenquist, 1995).
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Drilling requirements: Technology and Logistics
The volcanic rocks at the seafloor at both sites consist of strongly altered, slightly altered
and fresh basalts, trachybasalts and basaltic andesites. In the central zone of the summit plateau
at Conical Seamount, clay alteration assemblages have completely replaced the original basalt.
This alteration zone is expected to continue at depth. The Onsen site at Desmos Caldera is
further characterized by strong leaching of the basaltic andesites. No massive sulfides were
found at either site, although extensive subseafloor stockwork mineralization is expected at
depth. The vertically extensive nature of subaerial epithermal systems suggests that most of the
mineralization will occur in highly telescoped vein networks that may extend for at least 300-500
m below the seafloor.
Based on experience from Leg 158 (TAG Hydrothermal Mound, Humphris et al., 1995;
Herzig et al., 1998b) drilling in fresh and altered volcanic rocks as well as in talus and breccias
may be facilitated by use of the motor driven core barrel (MDCB) or rotary core barrel (RCB)
coring system, setting casing through the unstable sections of altered volcanics (usually the upper
part) and use of logging tools that can be run through casing or logging-while-drilling (LWD)
technique. The side entry sub (SES), which obtains logs while the drill pipe is removed, should
also be considered. To access the suspected styles of alteration and mineralization, it is planned
to drill one 400 m and two 200 m holes at each site. For the deep (400 m) holes, logs will be run
using standard (triple-combo and FMS-sonic) as well as special tools such as geochemical, high-
temperature and magnetic susceptibility tools. Conical Seamount is currently inactive, both
volcanically and hydrothermally. The summit plateau is generally only slightly sedimented
(some centimetres) and largely made up of basaltic rocks. There is no potentiial hydrocarbon
risk involved.
RCB drilling down to about 400 m including setting of a reentry guide base, casing, and
logging will take about 14 days at Conical Seamount (1.050 m) and 15 days at Desmos Caldera
(1.930 m). RCB drilling of two holes down to 200 m at each site without reentry guide base,
casing, and logging will take 3.5 days at Conical and about 4 days at Desmos. The total
requirement for drilling time is 44 days. A suitable port for embarking and disembarking of
13
scientific and technical personal is Rabaul, New Britain (Papua New Guinea). Conical
Seamount is located in a distance of about 170 nm and Desmos Caldera approximately 35 nm
from Rabaul. Both Conical Seamount and Desmos Caldera are located in territorial waters of
Papua New Guinea. Since 1994, we have developed a good relationship with the Geological
Survey of Papua New Guinea, the University of Papua New Guinea, and the Institute of PNG
Studies, all at Port Moresby.
Site Surveys
High resolution DGPS bathymetry (published as GSC Open File Report No. 3718).
Single channel seimic lines covering the surrounding areas.
Heat flow survey at Conical Seamount.
Extensive camera-video coverage.
Comprehensive TV-grab and dredge sampling
Hydrocast sampling.
Sediment cores in the general area.
Submersible surveys and sampling of hydrothermal fluids at Desmos with Shinkai 6500
of JAMSTEC (GSA Data Repository item 9708).
A pre-site survey using the R/V Sonne and the BRIDGE Rock Drill of the British
Geological Survey (Edinburgh) is planned for 2002 but subject of approval by the respective
review committee. During this 15 day-cruise it is anticipated (based on previous experience of
the BGS group at Edinburgh) to drill and core (49 mm diameter) a total of about 50 shallow (up
to 5 m) holes to better define the drilling targets for the proposed ODP drilling.
14
Binns, R.A., Parr, J.M., Scott, S.D., Gemmel, J.B. and Herzig, P.M., 1995. PACMANUS: an
active siliceous volcanic-hosted hydrothermal field in the eastern Manus Basin, Papua New
Guinea. Australian Institute of Mining and Metallurgy, 9/95: 49-54.
Binns, R.A. and Scott, S.D., 1993. Actively forming polymetallic sulfide deposits associated
with felsic volcanic rocks in the eastern Manus back-arc Basin, Papua New Guinea. Economic
Geology, 88: 2226-2236.
Farr, L.C., Perfit, M.R., Heatherington, A., Jonasson, I.R., Hannington, M., and Herzig, P.
Petrology and geochemistry of alkaline lavas and associated hydrothermal deposits from
seamounts in the Tabar-to-Feni Island arc: Papua New Guinea. American Geophysical Union
Annual Meeting, San Francisco, EOS (Trans. Am. Geophys. Union) 80 (45): in press.
Gamo, T., Okamura, K., Charlou, J.-L., Auzende, J.-M., Ishibashi, J., Shitashima, K., Chiba, H.,
and shipboard scientific party of ManusFlux cruise, 1997. Acidic and sulfate-rich
hydrothermal fluids from the Manus back-arc basin, Papua New Guinea. Geology, 25(2): 139-
142.
Gemmell, J.B., Binns, R.A. and Parr, J.M., 1999. Submarine, high sulfidation alteration within
DESMOS caldera, Manus Basin, PNG. In Stanley (Editor), Mineral Deposits: Processes to
Processing. Balkema, London: 503-506.
Glasby, G.P., 2000. Lessons Learned from Deep-Sea Mining. Science, 289: 551-553.
Hannington, M.S., Poulsen, K.H., Thompson, J.F.H., and Sillitoe, R.H., 1999. Volcanogenic
gold in the massive sulfide environment. Reviews in Economic Geology, 8: 325-356.
Hedenquist, J.W., Izawa, E., Arribas, A., and White, N.C., 1996. Epithermal gold deposits:
Styles, characteristics, and exploration. In S.o.R. Geology (Editor), Resource Geology Special
Publication Number 1. Komiyama Printing Co., Tokyo: 165-182.
Hedenquist, J.W., and Lowenstern, J.B., 1994. The role of magmas in the formation of
hydrothermal ore deposits. Nature, 370: 519-527.
Herzig, P.M., Hannington, M., Stoffers, P., Arribas, A., Becker, K.-P., Binns, R., Browne, P.,
Gennerich, H.-H., Hartmann, M., Heesemann, B., Hefter, J., Jonasson, I., Kila, R., Lange, S.,
McInnes, B., Meyers, J., Percival, J., Petersen, S., Pichler, T., Rosenberger, A., Ruggieri, G.,
15
Schott, T., Schwarz, U., Seifert, R., Vcillinger, H., Winn, K., 1994. Tectonics, Petrology and
Hydrothermal Processes in Areas of Alkaline Island-Arc Volcanoes in the Southwest Pacific:
The Tabar-Lihir-Tanga-Feni Island Chain, Papua New Guinea. Cruise Report SO-94: 273 pp.
Herzig, P.M., and Becker, K.-P. (eds), 1996. Tectonics, Petrology and Hydrothermal Processes
in Areas of Alkaline Island-Arc Volcanoes in the Southwest Pacific: The Tabar-Lihir-Tanga-
Feni Island Chain, Papua New Guinea. Final Report SO-94: 289 pp.
Herzig, P.M. and Hannington, M.D., 1995. Hydrothermal activity, vent fauna, and submarine
gold mineralization at alkaline fore-arc seamounts near Lihir Island, Papua New Guinea.
Proceedings Pacific Rim Congress 1995, Australasian Institute of Mining and Metallurgy:
279-284.
Herzig, P.M., Hannington, M.D., McInnes, B., Stoffers, P., Villinger, H., Seifert, R., Binns, R.,
Liebe, T., and Scientific Party, 1994. Submarine alkaline volcanism and active hydrothermal
venting in the New Ireland forearc basin, Papua New Guinea. EOS 75: 513-516.
Herzig, P., Hannington, M., Stoffers, P., Becker, K.-P., Drischel, M., Franz, L., Gemmell, B.,
Höppner, B., Horn, C., Horz, K., Franklin, J., Jellineck, T., Jonasson, I., Kia, P., Mühlhan, N.,
Nickelsen, S., Percival, J., Perfit, M., Petersen, S., Schmidt, M., Seifert, T., Thiessen, O.,
Türkay, M., Tunnicliffe, V., and Winn, K., 1998. Volcanism, Hydrothermal Processes and
Biological Communities at Shallow Submarine Volcanoes of the New Ireland Fore-Arc
(Papua New Guinea). Cruise Report SO-133. 146 pp.
Herzig, P.M., Hannington, M.D., Stoffers, P. and shipboard scientific party, 1998a. Petrology,
Gold Mineralization and Biological Communities at Shallow Submarine Volcanoes of the
New Ireland Fore-Arc (Papua-New Guinea): Preliminary Results of R/V Sonne Cruise SO-
133. InterRidge News, 7(2): 34-38.
Herzig, P.M., Humphris, S.E., Miller, D.J., and Zierenberg, R.A. (Eds.), 1998b. Proceedings of
ODP, Scientific Results, 158: College Station, TX (Ocean Drilling Program).
Herzig, P.M., Petersen, S., and Hannington, M.D., 1999. Epithermal-type gold mineralization at
Conical Seamount: a shallow submarine volcano south of Lihir Island, Papua New Guinea. In
16
Stanley, C.J. et al., Mineral Deposits: Processes to Processing, Proceedings of the Fifth
Biennial SGA Meeting and the Tenth Quadrennial IAGOD Symposium London: 527-530.
Humphris S.E., Herzig P.M., Miller D.J., Leg 158 Shipboard scientific party, 1995. The internal
structure of an active sea-floor massive sulphide deposit. Nature, 377: 713-716.
Kennedy, A.K., Grove, T.L., and Johnson, R.W., 1990a. Experimental and major element
constraints on the evolution of lavas from Lihir Island, Papua New Guinea. Contrib Mineral
Petrol., 104: 722-734.
Kennedy, A.K., Hart, S.R., and Frey, F.A., 1990b. Composition and isotopic constraints on the
petrogenesis of alkaline arc lavas: Lihir Island, Papua New Guinea. Journal of Geophysical
Research 95(5): 6929-6942.
McInnes, B.I.A., and Cameron, E.M., 1994. Carbonated, alkaline metasomatic melts from a sub-
arc environment: Mantle wedge samples from the Tabar-Lihir-Tanga-Feni arc, Papua New
Guinea, Earth Planet Sci. Letts., 122: 125-141.
McInnes, B.I.A., Gregoire, M., Binns, R.A., Herzig, P.M., and Hannington, M.D., 2000.
Hydrous metasomatism of oceanic sub-arc mantle, Lihir, Papaua New Guinea. Part I.
Petrology and geochemistry of fluid-metasomatised mentle wedge xenliths: Earth Planet. Sci.
Letts. (submitted).
McInnes, B.I.A., McBride, J.S., Evans, N.J., Lambert, D.D., and Andrew, A.S., 1999. Osmium
isotope constraints on ore metal recycling in subduction zones: Science, v. 286, p. 512-517.
Moyle, A.J., Doyle, B.J., Hoogvliet, H., and Ware, A.R., 1990. Ladolam gold deposit, Lihir
Island. In Hughes, F.E. (ed) Geology of the Mineral Deposits of Australia and Papua New
Guinea 2: 1793-1805.
Müller, D. and Groves, D.I., 2000. Potassic Igneous Rocks and Associated Gold-Copper
Mineralization. Springer, Berlin, 252 pp.
Patterson, D.B., Farley, K.A., and McInnes, B.I.A., 1997. Helium isotopic composition of the
Tabar-Lihir-Tanga-Feni island arc, Papua New Guinea. Geochem Cosmochem Acta 61: 2485-
2496.
Port Moresby Geophysical Observatory, 1994. Earthquake map of the PNG region 1964-1994.
17
Petersen, S., Herzig, P.M., Hannington, M.D., and Jonasson, I.R. Submarine epithermal-style
gold mineralization near Lihir Island, New Ireland fore-arc, Papua New Guinea. submitted to
Economic Geology.
Sillitoe, R.H., 1983. Enargite-bearing massive sulfide deposits high in porphyry copper systems.
Economic Geology, 78: 348-352.
Sillitoe, R.H., 1994. Erosion and collapse of volcanoes: causes of telescoping in intrusion-
centered ore deposits. Geology, 22: 945-948.
Sillitoe, R.H., Hannington, M.D., and Thompson, J.F.H., 1996. High-sulfidation deposits in the
volcanogenic massive sulfide environment. Economic Geology, 91: 204-212.
Stracke, A., 1996. Geochemie von Seamount-Basalten und Inselbogen-Vulkaniten der Tabar-
Lihir-Tanga-Feni-Inselkette, Papua New Guinea. Unpubl. MSc Thesis University of
Tübingen, Germany: 79 pp.
White, N.C. and Hedenquist, J.W., 1995. Epithermal Gold Deposits: Styles, Characteristic and
Exploration. SEG Newsletters, 23: 159-164.
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Figure 1. Simplified regional geological map showing the location of the major tectonic elements
in the New Ireland/Bismarck Sea region and the location of Conical Seamount (close to
Lihir Island) and Desmos Caldera (close to New Ireland). Note that Conical Seamount is
situated in a fore-arc position relative to the Manus-Kilinailau subduction zone, whereas
Desmos Caldera occupies a back-arc position relative to the New Britain trench.
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