Interactive comment on “ The location of lithospheric-scale transfer faults and their control on the Cu-Au deposits of New Guinea ” by L . T

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Introduction
The exploration for metalliferous deposits around the world presents a challenge as there is still much to learn about the processes that concentrate metals in particular areas.Many of the largest mineral deposits around the world were found from detailed Figures exploration campaigns around areas where the "old timers" panned the streams and sunk shafts, particularly in the search for gold.There is a major geological challenge however, in understanding the bigger picture, and why there are regions of the globe that are particularly well endowed with concentrations of precious metals.In the pursuit of this goal, geologists typically devise models that attempt to explain why some metals are more concentrated in particular regions.One such model is that gold and copper deposits are often found along strike of other deposits (e.g.along a line, or a lineament) (cf.Richards et al., 2000).However, the problem here, is that several deposits must be discovered before a line can be drawn between the points.So, lineaments are only proposed retrospectively, after several deposits have been identified.The effectiveness of this technique is questionable.Yet, these lineament style analyses are commonly used by the minerals exploration industry, particularly on the island of New Guinea because it is home to some of the world's richest copper-gold porphyry and epithermal deposits (e.g.Grasberg, Ok Tedi, Frieda River, Porgera and Wafi-Golpu) (Fig. 1a).
The idea that New Guinea was dissected by a series of arc-normal transfer faults was first proposed in Hill (1991).This model drew on the idea that northern Australia had a dominant NNE-SSW oriented crustal fabric that ran across the Arafura Sea and into southern New Guinea (Fig. 1b) (A. P. C., 1961) where the faults were said to be reactivated lateral ramps that formed during a period of shortening during the Neogene, displacing earlier formed extensional faults.This structural interpretation was also proposed to explain results from apatite fission-track analyses which indicated that different parts of PNG had experienced varying rates of uplift (Hill and Gleadow, 1989).
Further support for the model was provided by Davies (1990Davies ( , 1991) ) who showed that NNE-SSW striking clusters of mantle-derived intrusives and volcanics occurred near Bosavi (Fig. 2a).This chain of igneous rocks is referred to as the "Bosavi Lineament" (Davies (1990(Davies ( , 1991)).A second magmatic lineament was also identified to the east, drawn through Anju (south) to Ananadi (north) (Fig. 2b).As the magmatic centres along these lineaments young to the south, Davies (1990) calculated that the magmatic front migrated at a rate of 5-8 mm per year (Fig. 2c and d).This rate of movement is an Introduction

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Full order of magnitude lower than that of the Australian plate (e.g.DeMets et al., 1990), so this magmatism was said to be controlled by a local decrease in pressure in the mantle beneath a deep crustal tensional structures oriented parallel to the axis of maximum horizontal stress (i.e. a NNE-SSW striking transfer fault) (Davies et al., 1990).It was not long before more arc-normal transfer structures were proposed to exist in New Guinea, east and west of those that were identified by Hill (1991) and Davies et al. (1990Davies et al. ( , 1991)).These arc-normal structures were defined on the basis of the interpretation of gravity data and the orientation of geomorphological features such as drainage lines identified from Landsat imagery and aerial photography (Fig. 1c) (e.g.Dekker et al., 1990;Corbett, 1994;Kendrick et al., 1995;Gow and Walshe, 2005).Several workers then drew on the link between the structural and magmatic lineaments (e.g.Hill, 1991;Davies et al., 1990Davies et al., , 1991) ) and the location of some of New Guinea's copper and gold deposits.The NNE-SSW striking lineaments were considered to dilate perpendicular/obliquely to the regional maximum principal stress direction associated with convergence between the Australian and Pacific plates.These dilationary zones were said to focus the ascent of evolved magmas and magmatic and metalliferous fluids from deep-crustal reservoirs to nearer the Earth's surface (e.g.Corbett, 1994;Kendrick et al., 1995;Hill et al., 1996Hill et al., , 2002;;Richards, 2000).It did not take long before a NNE-SSW striking lineament was identified to intersect each copper and gold deposit found in New Guinea (Corbett, 1994;Kendrick et al., 1995;Hill et al., 2002;Gow and Walshe, 2005) (Fig. 1c).These were proposed according to the interpretation of various data.Yet, while there has been much interest in mapping the arc-normal transfer structures, it is difficult to evaluate if they actually exist.This is because the data that were used to interpret the structures is often not presented, or if data were shown, the resolution/quality was too low to clearly interpret the location of a geological structure.We were therefore skeptical as to whether the proposed transfer structures exist in New Guinea, and were curious as to whether these structures were mappable using higher resolution geophysical data which was not available when the lineament concept was Introduction

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Full originally proposed.We therefore discuss the background behind the concept of the lineaments in New Guinea and evaluate the earlier lineament interpretations against modern geophysical datasets.

Geophysical data that was used in this study
In this section we discuss the data that were used, including information about the source and resolution of the data, as well as how the data was processed and interpreted.Please note that we were unable to access the same gravity and magnetic data that were used in the earlier studies, so we instead used publicly accessible data, or data that we obtained permission to use.

Topography/bathymetry
Several workers proposed lineaments on the basis of interpretations of topographic data (Corbett, 1994;Kendrick et al., 1995;Gow and Walshe, 2005).We obtained topographic data for New Guinea from the Global Multi-Resolution Topography (GMRT) model (Ryan et al., 2009) (Fig. 3) as well as the Consultative Group on International Agricultural Research Consortium for Spatial Information (CGIAR-CSI) who reprocessed NASA's Shuttle Radar Topographic Mission (SRTM) global digital elevation dataset (Version 4.0) (Jarvis et al., 2008) (Fig. 4).
The spatial resolution of the GMRT is variable as it ties together multiple sources of data.The resolution of the onshore topography data ranges between 30 m and 90 m, whilst the resolution of bathymetric data is generally ∼ 100 m (and up to ∼ 50 m in some coastal areas).In comparison, the CGIAR-CSI SRTM data has a uniform resolution of 90 m, but the coverage is limited to land above sea level.The variable ∼ 30-100 m resolution of these data indicate that structural features can be mapped to a sufficient level of detail for a regional interpretation such as presented here, that is, provided that these geomorphological features actually represent faults.Introduction

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Full The GMRT data was manipulated online using GeoMapApp (www.geomapapp.org).The CGIAR-CSI SRTM data is served as a series of tiles to the community from CGIAR-CSI's website (http://srtm.csi.cgiar.org).The relevant tiles were downloaded and were merged using ArcGIS 10.0.
We used the GMRT dataset (Ryan et al., 2009) to assess whether lineaments could be observed in regions such as the Arafura Sea between Australia and New Guinea (e.g.Fig. 3).We used the SRTM data to evaluate the interpretation of Gow and Walshe (2005), who proposed that some NE-trending lineaments could be identified in PNG if only the 10 m, 100 m and 1000 m topographic contours were drawn on a map (Fig. 4a).
To do this we orthorectified the map that was shown in Gow and Walshe (2005) and compared this with the same selection of topographic contours generated from the SRTM data and displayed in ArcGIS (Fig. 4b).

Magnetics
To our knowledge there are no publicly available regional onshore magnetic datasets that cover New Guinea, so we could not produce a structural interpretation for the island.The EMAG2 Earth Magnetic Anomaly Grid (Maus et al., 2009) covers much of the offshore region that surrounds New Guinea (see Supplement file 1), and Geoscience Australia continue to publish maps of their compiled magnetic datasets (e.g.Milligan, 2010), but these do not extend far enough to the north to be useful for a structural interpretation of onshore New Guinea.These datasets do provide useful information about the orientation of fabric(s) along northern Australia so these were used in conjunction with gravity data (see Sect. 2.3) to assess the orientation of lineaments along northern Australia, the Arafura Sea and southern New Guinea (Fig. 1d).
We were fortunate to be provided with two high-resolution aero-magnetic datasets that covered parts of the PNG Central Highlands and the Papuan Peninsula (Figs. 3     and 5).These data were collected in north-south oriented lines with 400-500 m line spacing and a terrain clearance of 100 m during a helicopter-borne survey conducted by Fugro Ltd. between 2006 and 2008.The aero-magnetic data grids have a cell size Introduction

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Full of 100 m by 100 m such that these data can effectively show magnetic anomalies with wavelengths of 200 m.A raster was produced from the magnetic data using a minimum curvature, exploration industry standard interpolation.The Central Highlands dataset covers an area that encompasses the Porgera, Mt Kare and Yandera Cu-Au deposits (Fig. 5), and therefore the northern segment of the Porgera-Mt Kare lineament (Hill, 1991).So, these data were used to determine if these lineaments could be identified with regional magnetic data.This involved an examination of the reduced-to-pole magnetic grid.We also examined the same grid after applying an Upward Continuation Residual (UCR) filter (Jacobsen, 1987;Morse, 2010).The UCR filter is a method of frequency separation that generates a high frequency residual dataset by subtracting a higher upward continued (UC) potential field dataset from a lower UC or original (zero level) of the same dataset.Upward continuation simulates the effect of measuring the potential field at a higher (larger) distance from the source (ground level), so this calculation effectively filters out the anomalies of smaller and shallower sources, producing a smoother, longer wavelength dataset (a higher UC produces a smoother the dataset relative to a lower UC).The high frequency signal in an UC or original dataset can be accessed by subtracting the higher, smoother (longer wavelength) upward continued signal.This arguably produces a dataset that shows significantly enhanced geological features (Morse, 2010).In this case, we generated new grids by subtracting: (1) the 1 km upward continued (UC) grid from the original magnetic data grid, (2) the 5 km UC grid from the 1 km UC magnetic data grid, and (3) the 5 km UC grid from a 2 km UC magnetic data grid (Fig. 5).

Gravity
In addition to the examination of topographic and magnetic datasets, we also interpreted free-air and Bouguer gravity grids to determine if these data could be used to delineate arc-normal transfer faults (Fig. 6).The grids used were spatial subsets of the global Earth Gravitational Model (EGM2008) (Pavlis et al., 2008), covering the greater New Guinea region.These data were downloaded from the Bureau Grav-Introduction

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Full imétrique International's (BGI) data portal (http://bgi.omp.obs-mip.fr/data-products/Grids-and-models/regional_gravity_anomaly_grids).The Bouguer data that was downloaded had been corrected using the FA2BOUG code that was proposed by Fullea et al. (2008).This included a topographic correction that was applied up to a distance of 167 km using the 1.0 × 1.0 arcmin ETOPO1 Digital Elevation Model (Amante and Eakins , 2009).The gravity data has a spatial resolution of 2.5 × 2.5 arcmin (∼ 4-5 km).While this is quite coarse, it is the best publicly available data (to our knowledge) that covers onshore New Guinea.This data was used to produce a raster with a minimum curvature interpolation.
The upward continuation residual (UCR) filter (see Sect. 2.2) (Jacobsen, 1987;Morse, 2010) was also applied to the Bouguer dataset.In the case of the UCR Bouguer gravity data, new UCR grids were generated by subtracting the original Bouguer gravity grid upward continued X kilometres above the surface, from the same grid upward continued Y kilometres above the surface, [i.e.grid(Y ) minus grid(X )] (Figs.7-8).The X and Y heights for the UCR grids that were generated are shown in Table 1.

Additional image processing of magnetic and gravity data prior to structural interpretation
The magnetic and gravity datasets were loaded in ER Mapper 7.1 before any structural interpretation began.Three duplicate gravity or magnetic images were draped on top of one another.The base layer was used to display the "intensity" of the magnetic or gravity signal.The intensity layer was illuminated with a light source from the north (000

Seismic tomography
Seismic tomography has proven a useful tool to map geological structures in the lower crust and mantle.We used the global P wave seismic tomography dataset of Li et al. (2008) and the global S wave seismic tomographic dataset of Debayle et al. (2005) to determine if any arc-normal lineaments were imaged with tomography data and therefore major crustal structures since these structures reportedly focus Cu-Au bearing fluids from such depths (Corbett, 1994;Kendrick et al., 1995;Hill et al., 1996Hill et al., , 2002)).The tomographic data were imported as a grid of points into ArcGIS 10.0.Tomograms were produced by applying a spline interpolation to the point data for different depth slices (68 km, 113 km and 203 km) (Fig. 11).The data were also contoured at discrete intervals to aid the identification of any linear structural features (Fig. 11).
The spatial resolution of this dataset is estimated to be ∼ 100 km in the best sampled regions of the upper mantle (Li et al., 2008).The station coverage is relatively good across New Guinea and northern Australia (cf.Fig. 1 of Li et al., 2008), but as this coverage is less dense than other parts of the world, the spatial resolution is likely to be greater than 100 km.This means that the tomography data will not be useful in identifying a particular fault or lineament in New Guinea, but it should still be useful in identifying if there are any major discontinuities in the lower crust and upper mantle.

Topographic data
Our examination of the GMRT bathymetric and topographic data did not identify any regional NE to N striking lineaments in northern Australia, the Arafura Sea or in New Guinea (Fig. 3).We were also unable to identify any clear NE to N striking lineaments using SRTM data when using all of the data, or with selected contours as advocated by Gow and Walshe (2005).Our regional comparison is shown suggested that NNE-trending lineaments could be readily identified when the 10 m, 100 m and 1000 m topographic contours were drawn (Fig. 4a), but this is not evident when the same contours are drawn using the SRTM data (Fig. 4b).This means that the contours that were used by Gow and Walshe (2005) were smoothed or were derived from topographic data with a much lower spatial resolution.Considering these points, we concluded that topographic data is not the best data to use to discriminate arcnormal lineaments.So, it was not used any further in this study.

Magnetics
The regional magnetic data UCR grid shows that the original regional magnetic data contains many subtle N-S to NW-SE oriented lineaments (Fig. 5a and b).We are unsure as to whether these lineaments represent orthogonal/polygonal faults (Fig. 5a  and b), chevron-type folds (Fig. 5b), if they reflect a topographic feature, or if these do not represent geological features, and are a data artefact.As these lineaments are not visible in the lower frequency UCR filtered data (Fig. 5c and d), it indicates that they do not occur deep in the crust.
We also observed several subtle NE striking magnetic features in the region directly east of Porgera (Fig. 5e).These lineaments were also not imaged in the lower frequency UCR grids, indicating that they are not deep structures (Fig. 5f).We suspect that these lineaments could represent shallow dykes, veins or fractures given that they were only observed around volcanic centres (Fig. 5e).
Although there are possible NNE striking faults and dykes, these are subtle structural features.We envisaged that the lineament that was proposed to intersect the Mt.Kare and Porgera Cu-Au deposits (Corbett, 1994;Kendrick et al., 1995) would be more pronounced in magnetic data.However, these data indicate the Mt.Kare/Porgera lineament is not a magnetic feature, or that this particular lineament does not exist (Fig. 5a).Introduction

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Gravity
The free-air and Bouguer gravity data indicate that NNE trending lineaments occur in various regions of New Guinea (Fig. 6a and b).Yet these images also show that there are many other lineaments with different orientations.This is particularly the case along the northern margin of Australia, the Arafura Sea and southern New Guinea where N-S oriented lineaments are more pronounced than lineaments with other orientations (Figs.1d, 6a and b).
The transfer faults that were proposed by Hill (1991) and Kendrick et al. (1995) were overlain on the free-air and Bouguer gravity data.This shows that some of the previously proposed NNE trending lineaments correspond with sharp boundaries in the gravity data, yet many of the proposed lineaments do not (Fig. 6a and b).
While there are some lineaments that are apparent in all of the gravity grids, for example, the N-S to NE-SW oriented structures that cut across the Arafura Sea into southern New Guinea (Fig. 6).We found that it was much easier to identify lineaments in the UCR filtered gravity grids relative to the free-air and Bouguer gravity data.The UCR filtered images highlight distinct edges of gravity anomalies, many of which could be interpreted as lineaments, and indeed arc-normal transfer faults (Figs. 7 and 8).Some of these distinct breaks in gravity anomalies correspond with the lineaments proposed by earlier workers (e.g.Hill, 1991;Kendrick et al., 1995).Some of the distinct changes in gravity could also be interpreted as faults, as they show an apparent sense of displacement (Fig. 9).

A revised regional lineament map from the interpretation of gravity data
An updated lineament map of New Guinea was produced by examining each of the UCR filtered magnetic and gravity grids (Fig. 10).These grids indicate that NNE trending lineaments do occur in New Guinea, particularly in the central and northern parts of the island.However, these structures are not as laterally extensive as earlier workers proposed.The geophysical data also indicate that there are multiple orientations Introduction

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Full of fabrics in the northern Australian lithosphere, and this conflicts with the idea that there is a pervasive NNE fabric between northern Australia and New Guinea (e.g.Fig. 1c).This indicates that the lineaments observed in New Guinea are not related to those in northern Australia, or that the older structures of the Australian lithosphere have been folded or rotated into their current orientation.Our structural interpretation also indicates that only some of the Cu-Au deposits overlie (or at least proximal to) an arc-normal lineament (Fig. 10/Table 2).These include Star Mountain, Ok Tedi, Hidden Valley, Edie Creek, Mt.Bini and possibly Grasberg.It is interesting to note that these deposits are relatively young (< 4.5 Ma) and the deposits that are older than 4.5 Ma do not correspond with arc-normal structures (Table 2).

Seismic tomography
The P wave seismic tomography grids show that there is a NE-SW to N-S oriented boundary between what we interpret to represent cold Australian lithosphere (Fig. 11).This boundary is most pronounced in the 113 km and 203 km depth tomograms (Fig. 11b-f), but it is also visible in the 68 km depth slice.The tomographic feature is also imaged at the same depths in the global S wave tomographic dataset of Debayle et al. (2005) (Supplement data file 2).We are confident that this tomographic anomaly represents a lithological/mantle structure as it is imaged in multiple tomographic datasets.When our revised lineament interpretation (Fig. 10) is overlain on the 68 km, 113 km and 203 km tomograms (Fig. 11b, d and f) it clearly shows that several NNE trending lineaments follow the western edge of the tomographic anomaly (Fig. 11b, d and f).
It is therefore possible that the geometry of this mantle structure could control the orientation of faults/lineaments observed at, or near the surface.Introduction

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Structural interpretation of geophysical data
The application of a UCR filter to gravity and magnetic data was useful for interpreting lineaments when compared to using the original free-air gravity, Bouguer gravity and reduced-to-pole magnetic data.The use of different sun-angle orientations to highlight lineaments of different orientations was an essential part of the process.This is because regional structural interpretations of geophysical images where only one sunangle orientation is used will bias which structures are drawn/interpreted.While the geophysical data does not prove that a lineament is a geological structure (e.g. a fault), we are confident that many of the interpreted lineaments are geological structures as some of the gravity anomalies are offset (e.g.Fig. 9).However, it is also likely that some of the lineaments that were interpreted could reflect features that are not geological structures.Such issues will be refined through time as new, higherresolution data become available.

Arc-normal faults and their control on Cu-Au mineralization
Our aim was to present a methodical and systematic method of mapping lineaments in a way that the reader could clearly evaluate our work and come to their own judgement as to whether arc-normal faults exist in New Guinea.We were initially skeptical about the existence of any arc-normal transfer structures in New Guinea as the evidence that was proposed in support of these structures was often not shown, or was not clearly presented.However, our analysis of various geophysical data do indeed support that some arc-normal lineaments occur along the length of the island (Fig. 10).Hill (1991) proposed that arc-normal transfer structures developed in New Guinea after or during the Pliocene, where the orientation of the structures were controlled by a Proterozoic-Palaeozoic fabric with the same orientation along northern Australia, the Arafura Sea and New Guinea (Fig. 1b and c).However, our analysis of the trend

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Full of the basement fabric(s) in this region shows that there is much more variation in the orientation of these structures (Figs. 1d and 10) than what others had proposed earlier (Fig. 1b and c).This means that: (1) the arc-normal transfer structures are not related to the dominant structural grain of the Australian lithosphere; (2) that these structures are related to the dominant structural grain of the Australian lithosphere, but have been folded into their current orientation in New Guinea, (3) that the transfer faults are inherited from the Australian lithosphere, but the orientation of the structural grain was always different in New Guinea and Australia, or (4) that the arc-normal faults are unrelated to the any existing fabric and are associated with more recent orogenic events.It is therefore worth further consideration as to when these structures formed.Hill (1991) also proposed that the arc-normal transfer faults cut existing basement structures that first formed as extensional faults during the Late Cretaceous-Palaeocene (100-56 Ma), and were inverted during a phase of shortening in the Miocene (23-5 Ma).As the transfer structures cross-cut the inverted thrusts, it indicates that they formed during or after the Pliocene (5-0 Ma).This time constraint is interesting considering that we found that the transfer faults only intersect the Cu-Au deposits that are less than five million years old (Fig. 10 and Table 2).So, the Cu-Au deposits that are greater than five million years old cannot be related to arc-normal transfer structures.

Penetration depth of transfer faults
As the arc-normal lineaments were said to direct metalliferous fluids from deep in the crust, it was important to determine if these were deep faults.This is why we used various UCR filters on magnetic and gravity datasets, and why we looked at seismic tomography data.NNE trending lineaments were only observed in the higher frequency UCR filtered magnetic data, indicating that these particular structures are shallow features, or are not magnetic.The UCR filtered gravity data indicates that arc-normal lineaments are also mappable in the high-and low-frequency grids, suggesting that many of the arc-normal lineaments are significant structures that cut through deeper

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Full levels of the crust.This idea is supported by seismic tomography data that shows that the arc-normal structures might sole into deeper levels of the lithosphere and controlled by deeper lithospheric faults (Fig. 11).This indicates that the arc-normal faults could potentially tap mantle melts and fluids, and this is supported further by the field observations and geochemical data from chains of mantle derived melts and volcanoes (e.g.Davies, 1990Davies, , 1991)).It is therefore possible that the arc-normal transfer faults control the distribution of metals in New Guinea, but considering our other findings, perhaps only those that are less than five million years old.

Exploration under cover -mapping the intersection of intrusions and faults
One of the biggest challenges faced by mineral explorers today is the concept of finding new deposits that do not crop out at the surface.This is especially the case in regions that have very thick soil profiles or within heavily forested regions, such as in New Guinea.Gravity data has long been used as a tool for mineral explorers to infer information about the composition of the basement, where zones of low gravity typically reflect sedimentary basins or felsic intrusions.So we produced a map of the low gravity zones that were identified in the UCR filtered Bouguer gravity data in the hope that these zones represent zones of felsic to intermediate intrusions.The idea being that explorers might be able to focus their efforts on these regions as they could represent zones where hot metal bearing fluids and gases associated with magmatism were once deposited.To examine this, we used the 10-50 km UCR grid to ensure that we were effectively looking at the gravity signal from a depth of approximately 5 km, in the hope that the zones of lower gravity reflected igneous, rather than sedimentary rocks (Fig. 12a).This indicates that there are several areas that might represent future exploration targets (Fig. 12a).Explorers might be able to further concentrate their efforts on the low-gravity zones that are intersected by faults, or where faults occur above the gravity anomalies as the structures could act as conduits for fluids and gases, and thus zones where precious metals might come out of solution.

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Full However, there are several problems associated with this approach: (1) the resolution of the gravity data that was available to us is quite course (4-5 km), and (2) we do not have much in the way of geological control that could tell us more about the composition of the gravity anomalies.The first problem will only be resolved once more onshore gravity surveys are conducted on New Guinea.We addressed the second problem by comparing the position of low gravity zones with the Coordinating Committee for Geoscience Programs in East and Southeast Asia (CCOP) 1 : 2 000 000 geological map of SE Asia (downloaded from http://www.orrbodies.com/resources/item/orr0052),noting the location of felsic intrusives and extrusives and other lithologies at the surface.We then highlighted the areas where the felsic intrusives and extrusives intersected, or were near to the regions of low-gravity.While we understand that this cannot be adequately tested here, we considered it useful to include this approach, as well as a map so that this might be tested further in the future.

Conclusions
Our interpretation of the several different geophysical data types indicates that arcnormal lineaments do occur in New Guinea, but these structures are not as prevalent or as simple as they have previously been portrayed.Our approach in using these different data sets means that our interpretation covered some three orders of magnitude in terms of scale (topographic and magnetic data at ∼ 100 m ( 102 ); gravity data at 5 to 10 km (∼ 10 3 -10 4 ); and tomography data at 100 km (10 5 )).The lineaments were not identified in the highest resolution data and data representing the shallowest levels of the crust (e.g.topographic and magnetic data), however, there was evidence of arcnormal lineaments in the lower resolution data that imaged deeper levels of the crust (gravity and tomography).Though, our results show that these lineaments do not intersect every New Guinea Cu-Au deposit.Instead, it is only the copper-gold deposits that are less than five million years old that might be associated with arc-normal structural features.These findings mean that exploration geologists might be able to better target Introduction

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Full  Full  Kendrick et al. (1995), Corbett (1994), Dekkar et al. (1990) and Elliot (1994)  (c) the location of lineaments that were identified by different studies conducted along the length of New Guinea (Hill et al., 1991;Corbett et al., 1994;Dekkar et al., 1994;Kendrick et al., 1995).These interpretations assumed that NNE striking structures of the Australian mainland could be extrapolated across the Arafura Sea and into New Guinea (in this case the structures that are shown here for northern Australia were proposed by Elliot, 1994).(d) However, our interpretation of magnetic data (Milligan 2010: Magnetic Map of Australia, 5th Edition) and gravity data (Pavlis et al., 2008;2013;this paper) indicates that the orientation of the basement fabric is much more complex than previous workers proposed.* Mineralization ages were taking from the compilation of Garwin et al. (2005).* * Image was adapted from a figure presented in Hill et al. (1996).Introduction

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Full  Davies (1990Davies ( , 1991) ) who showed that magmatism in this region progressed from north to south across Papua New Guinea.This pattern is observed (a) locally where active volcanism occurs at Mount Bosavi and in smaller eruptive centres to the south, and (b) regionally.Davies (1990)  Bouguer and the various UCR filtered gravity datasets.We also compared these interpretations with structural information that was interpreted from the global multi-resolution topographic dataset (Ryan et al., 2009).Here we show the lineament map and the location of major Cu-Au deposits draped over the 10 km minus 50 km UCR filtered gravity grid (illuminated from the southeast).This figure shows that the location of some of the Cu-Au deposits (white circles) correlated with identifiable lineaments (transfer faults?), but it also shows that not every deposit is linked with an arc-normal lineament.Introduction

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Full Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | east (090 • ) and southeast (135 • ) with an inclination angle of 30-40 • so that we could highlight different orientations of geological structures, where a new image file was generated for each sun-angle.The middle and highest layers are duplicate images shaded with a gradient fill.The only difference between the two layers is that the highest layer was made partially transparent to better enhance the data in shadowed areas.Discussion Paper | Discussion Paper | Discussion Paper | Fig. 4. Gow and Walsh Introduction Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | d) Our interpretation of potential field data indicates that the orientation of the basement fabric(s) is more complex c) Lineament interpretation according to

Fig. 1 .
Fig. 1.Maps of northern Australia and New Guinea showing: (a) the location of major gold and copper deposits and the age of mineralization; (b) the location of lineaments according to the Australian Petroleum Company(A.P. C., 1961), who suggested that the basement fabric of northern Australia persisted across the Arafura Sea and into southern Papua New Guinea; (c) the location of lineaments that were identified by different studies conducted along the length of New Guinea(Hill et al., 1991;Corbett et al., 1994; Dekkar et al., 1994;Kendrick et al., 1995).These interpretations assumed that NNE striking structures of the Australian mainland could be extrapolated across the Arafura Sea and into New Guinea (in this case the structures that are shown here for northern Australia were proposed byElliot, 1994).(d) However, our interpretation of magnetic data(Milligan 2010: Magnetic Map of Australia, 5th Edition) and gravity data(Pavlis et al., 2008; 2013; this paper)  indicates that the orientation of the basement fabric is much more complex than previous workers proposed.*Mineralization ages were taking from the compilation ofGarwin et al. (2005).* * Image was adapted from a figure presented inHill et al. (1996).

Fig. 2 .
Fig. 2. The Bosavi Lineament was identified byDavies (1990Davies ( , 1991) ) who showed that magmatism in this region progressed from north to south across Papua New Guinea.This pattern is observed (a) locally where active volcanism occurs at Mount Bosavi and in smaller eruptive centres to the south, and (b) regionally.Davies (1990) drew to cross sections from Anandi to Anju and Chambri to Bosavi to show that (c and d) the volcanic front migrated at a rate of 6-8 mm yr −1 .Figure was modified fromDavies (1990).The basemap in (a) and (b) is from the Global Multi-Resolution Topography (GMRT) dataset(Ryan et al., 2009).

Fig. 8 .
Fig. 2. The Bosavi Lineament was identified byDavies (1990Davies ( , 1991) ) who showed that magmatism in this region progressed from north to south across Papua New Guinea.This pattern is observed (a) locally where active volcanism occurs at Mount Bosavi and in smaller eruptive centres to the south, and (b) regionally.Davies (1990) drew to cross sections from Anandi to Anju and Chambri to Bosavi to show that (c and d) the volcanic front migrated at a rate of 6-8 mm yr −1 .Figure was modified fromDavies (1990).The basemap in (a) and (b) is from the Global Multi-Resolution Topography (GMRT) dataset(Ryan et al., 2009).

Fig. 11 .
Fig. 11.Seismic tomograms were generated for the New Guinea region from a global P wave tomography dataset (Li et al., 2008).Here we show slices at different depths: (a-b) 68 km; (c and d) 113 km; and (e and f) 203 km.The images that are shown in the left hand column (a, c, e) have been contoured and also show the location of the Cu-Au deposits (white circles) that are described in Fig. 1a.The images that are shown in the right hand column(b, d, f) compare the tomography data with the lineament interpretation that is shown in Fig.9.There is some similarity between the orientation of some lineaments and the tomographic "anomalies".These tomography data also indicate that there is a keel of cold Australian lithosphere below much of western New Guinea.This possibly represents a rigid indentor.The Grasberg, Frieda River, Nena, Star Mountain and Ok Tedi deposits are located at the margins of this tomographic feature.This might indicate that the edges of the keel have influenced the location of faults in crust, and therefore helped to concentrate the deposition of metalliferous fluids/magmas.

Table 1 .
Details of the UCR grids that were generated from the BGI Bouguer gravity data where one upward continued grid (grid(X )) (that was generated by simulating the measurement being made X km above the original surface) was subtracted from another upward continued grid (grid(Y )) (that was generated by simulating the measurement being made Y km above the original surface).