IAEA-R-1442-F Geochemical Activation Analysis Surveys on Negors and Samar Islands in the Philippines

IAEA-R-1442-F

Geochemical activation analysis surveys on Negors and Samar Islands in the Philippines, (part of a coordinated programme on ncuelar based techniques in geology and mineral prospecting)

15 November 1973 - 14 November 1976

Gabriel Santos,Jr.

Philippine Atomic Energy Commission Chemistry Department Diliman, Quezon City Philippines

January 1977 ŒW/flED BY:

HEGROS AND SAMAP ISLANDS, PHILIPPINES

>•'.>

Gabriel Santos, Jr. Ofelia T. Palabrica Lourdes A. Guieb and Soledad B. Norcûa

Philippine Atomic Energy Commission Special Projects Division November, 19?6 ABSTRACT

A combination of neutron activation analysis and atomic absorption spectrometry was employed in two geocheiiical surveys. The first survey involved the determination of copper, scandium and cobalt in

hole rock (drill core) samples from southwestern Ne gros island while the second survey conducted in central Sauar island utilized pyrite as the sampling media. The elements analyzed in pvrite were copper, lead, zinc, vanadium, manganese and cobalt. The surveys were performed in areas w.ich contain disseninated (in Ner.roe) and massive (in Samar) copper minéralisations.

Statistical treatment of the ,eoc .e«dcal/anel;;tical data was

done to study the distributions of tlie elements of interest ?.rid to

determine the u;eocliemicai dependency of copper with the other ele-

ments. The correlation coefficients of Cu/Co and Cu/Sc in Hegros

rocks indicate slight-fair and low-inverse dependencies respectively.

Results from Samar survey reveal that that the close geochemical relationships of V, Pb, Co, and "ùa. with Cu exist. Thus, these ele-

ments can be used as indices or pathfinders in prospecting for

kuroko deposits in the Philippines using pyrite as the sampling

media. GEOCHEKICAL ACTIVATION ANALYSIS SURVEYS IN N2GR0S AND SAMAR ISLANDS, PHILIPPINES

INTRODUCTION

This work is part of a coordinated program on nuclear based techniques in geology and mineral prospecting under IAEA Research Contract No. 14^2. The research was carried out at the Philippine Atomic Energy Commission with one of us (G. Santos, Jr.) as the chief scientific investigator. The time covered by this final report is from November, 1973 to November, 19?6.

This project has for its objectives the following: (1) to study the geochemical relationships among scandium, cobalt and copper in drill core samples from Southern Negros

Island, (2) to relate the above geochemical relationships to occurrences of porphyry - type copper deposit in Hegros by statistical treatment; and (3) to determine the distribution of particular trace elements in the massive pyrite minerals of the Kuroko deposit found in Bagacay, Samar Island, It is felt that trace elements in pyrite can be used as possible Pathfinders in the search for Kuroko-type copper deposit.

Background and scope of the project. The discovery of new copper ore deposits will be enhanced by the identification of significant geochemical parameters at the outcrops and if possible in bore holes. Geochemical and geophysical explora- tory techniques are used to locate or narrow down mineralized zones from non-mineralized country rock. Meaningful correlations between the geochemical and geophysical characteristics may be obtained from the prospective area.-

An important factor in the interpretation of geochemical anomalies which are related with significant metal concentration — 2 — is the knowledge of the distribution of other associate elements in the host rock. The elements of interest in Kegros and Samar are copper (Cu), scandium (Sc) and cobalt (Co) in drill cores, and vanadium (V), lead (Pb) , cobalt (Co), manganese (Mn), copper (Cu), and zinc (Zn), in pyrite, respectively.

A magnetic survey of the Negros project areas was deemed necessary, because close association of magnetite with copper mineralization was noted»

"Kuroko" or black ore copper-zinc deposits which f re found in Bagacay, Sainar are massive sulfide type deposits that are similar to those widely distributed in Japan. Considering the close geographical location of the Philippines to Japan and certain similarities in their geologic environments, it is felt that there are good prospects for finding more kuroko deposits in the Philippines. However, very little geochemical inform- ation is available for this type of deposits in the country which can be used for the p;cochetnical prospecting of this important source of copper.

For trace element determinations in kuroko deposits, one of the most appropriate sampling media is pyrite (FeS_) because the deposits have very high pyrite content. Pyrite is also widely distributed throughout the various unmineralized rock units (except limestone) in the area. Thus, pyrite can provide an economically and easily collectible homogeneous materials. Furthermore, mineral sulfides are good collectors or carriers of trace elements thereby enhancing the sensitivity for the applicable analytical methods.

The Pro.ject areas. The first survey area is located on the island of Negros in Central Philippines at approximately - 3 -

122°41« longitude and 9°2O'?O" latitude and is about 133 km. by road west of Dumaguete City. Dumaguete City is about km. south of Manila. The investigated mineralized zone with an area of about 500 x 2000 meters is in Barrio haglinac, Basay, Negros Oriental. The location of this project area is shown in Figure 1 » Figure 2 is the geologic map of Basay area showing the drill holes. South of the investigated area to- wards the shoreline, the rocks consist of coral line limestone. According to Malicdem (1973) the age of the limestone is Pliocene. The regional structure of the country rocks trends to the North- west - Southeast. Copper mineralization occurs mainly in the dacite and diorites. The mineral sulfides in decreasing amounts are: pyrite (1-17%), chalcopyrite (1-2%) bornite and molybdenite. Magnetite is closely associated with the ferromagnesian minerals and occurs as disseminations in the rock.

The second project area is situated in the central part of Samar Island, also in Central Philippines at approximately 125°15f East longitude and 11Olf7' North latitude, with an area of about 3 sq. km. See Fig. 3« This survey c^rea is within the mining area of a private firm, Karinduque nining and Industrial Corporation (MMIC) in Barrio Bagacay, Kinabangan, Samar. Baga- cay Mines is about 56O km. southeast of Iianila.

Some preliminary studies on the geology and ore deposits in or near Bagacay mine area in Central Samar Island have been done by Kinkel et. al., (1956), Bryner (1967) and Balce and Esquerra (197*0. The geology of Bagacay mine area consists of silicified dacitic-ryholitic basement rocks which are unconform- ably overlain by altered - argillized dacite or dioritic and Pliocene clastic rocks. These rocks are in turn capped by Pliocene reef limestone. Kuroko type deposit or black ore which consists of high-grade copper-zinc ores are found within the clastic rocks and within carbonaceous sandy shale and argillized tuff. "Secondary" gossan separates the clastic rocks from the altered dacites or diorites which are for the most part completely argillized, Pyritization is generally widespread in all the rocks units except in the limestone. Figure k is the schematic geologic section of the Bagacay deposit. The principal nineral sulfide of the Bagacay ores are pyrite, chalcopyrite-bornite, sphalerite, chalcocite and minor galena. Snail amount of radio- active minerals can be found in sons argillized portions of the orebody and in the remnants of the primary gossan.

EXPERIMENTAL PART

A. Negros Island 1. Quantification of copper, cobalt and scandium. Drill core samples taken at intervals of 20-kO meters depth were analyzed. A total of one thousand four hundred fifty samples (1,450) were analyzed for copper making use of atomic absorption spectronetry. Ths copper analysis on 200 mg core samples was done by CDCP Mining Corp., assay laboratory at the project area. More than three hundred (300) representative samples were prepared and analyzed for scandium and cobalt using neutron activation analysis techniques described by Santos (1973)» These samples which were carefully chosen from the 1^50 samples were deemed sufficient to represent all the collected drill core samples. The statistical treatment of the geocheir.ical data used was described by Lepeltier (1969), Williams (I967)t and Tennant and White (1959). The statistical calculations h^.d been used in previous reconnaissance studies by Santos (1973). Cumulative frequency - 5 -

distribution curves for each analyzed element were made by plotting on a probability - log paper the concentration in parts per million (ppra) or percentage (%) of the element against the percent cumulative frequency (?.?CF). To measure the geochemical dependency of the analyzed elements with copper, correlation diagrams were constructed using the graphical method of Lepeltier. 2. Magnetic Survey. The ore deposits in the project area are mainly pyritic sulfide disseminations and fracture- filling in various associations with chalcopyrite, bornite, nagnetite and minor molybdenite. A microscopic study of those deposits revealed that sulfidcs and magnetites occur together in the copper ore deposits. To chock the observed close association of nagnetite with copper occurrenaenB, a magnetometer survey was conducted in the survey area, including the adjacent surrounding area. The magnetic method of geophysical surveying was planned on a grid pattern running in a north-south direction roughly intersecting the trend of the northwest striking orebody. A high precision magnetometer was used at picket locations to measure the vortical component of the magnetic field. Magnetic readings using a McPhar 700 M fluxgate magnetometer were taken every 25-meter distance interval. Field readings wore controlled for diurnal fluctuations using a base station every 2-k hours. A datum of approximately zero gamma for the base station was set. The field survey was performed by personnel of CDCP Mining who were trained by one of us (Santos) using the fluxgate magnetometer,

A total of 136 line-kilometers was staked at - 6 -

every 25 m. The measurements at each station were plotted. Magnetic vortical intensity profile was prepared for each line and a magnetic intensity contour map was constructed for the survey area. Contour interval is 100 gammas. Instrument accuracy was +5 gammas and diurnal control removed +10 gammas.

B. Samar Island Surface and pyrito stockpile samples weighing 1-2 kg. were collected from the pit and adjacent areas of Bagacay mines. The location of the survey area is shown in Figure 3- The samples were- crushed, pulverized and panned in running watur to remove the bulk of the low-density • . minorais. The heavy minerals were treated with bromoform to separate the sulfides from the gangue. Hand mr-tpjnets ' were used to remove the na^netito from the sulfides. About 50 mg» of the sulfides were separately packed in polyethylene bags and heat-sealed. The cor- responding standards, manganese dioxide (MnO_) and vanadium pent oxide (V-O,.) were likev/ise prepared. . The sulfide samples and standards v;;;re irradiated for three (5) minutes at the pneumatic tube system of the Phil- 12 —2 —1 ippine research reactor at a flux of 1 x 10 n.cm .sec . Activity measurements of the irradiated samples and standards wore made utilizing a 3" x 3" Nal(Tl) detector coupled to a 100-channel analyzer. The O.85 MeV photopeak of the 2.56 h Kn and 1J+3 KeV photopeak of the 3.77 m V were respectively used in the calculations of the manganese and vanadium contents of the sulfides. Another batch of the sulfide samples, weighing one (1) gram each, was dissolved in aqua regia and - 7 -

hydrochloric acid. These samples were analyzed for cobalt, copper, lead and zinc using atomic absorption spectrometry. Statistical treatment of the data was done by constructing cumulative frequency distribution curves for analyzed element and correlation diagrams between two elements.

RESULTS AND DISCUSSIONS

Negros Island 1. Quantification of copper, cobalt and scandium in Negros Oriental drill core samples. The distributions of copper, cobalt and scandium in the project area are essentially lognormal. The cumulative frequency diagrams in Figure 5 indicate that the three elements have an excess of lov; values» The background and threshold values are given in Table 1. The background for copper is within the range of the copper content of a typical copper porphyry deposit, Jerome ,(1966). The background and threshold values for cobalt, 18 ppm and kh ppm respectively are close to the values found in Bohol island and Davao in Mindanao island indicating the similarity of cobalt distributions in these regions. The background value for Co in this survey area is close to the 1^f ppm value given by Ahrens (1963) for basaltic rocks, but is much less than the median of 38 ppm Co for basalts as found by Prinz (1969). The background value for scandium in this survey area is slightly higher than the value found in Bohol and Davao. This difference may be due to the presence of copper mineralization and/or nature of the host rock. The computation of the correlation coefficient - 8 -

for the elements were obtained uting the methods of Lepeltier (1969)• Correlation coefficients of the elements in core drill samples from Negros Oriental are shown in Table 2. The correlation coefficient (O.^1*) of Sc-Co and its correlation diagram (Figure 6) suggest a less moderate dependency in the relationship of these two elements, while the Cu-Co corrélation coefficient (O.36) and correlation diagram (Figure 7) show slight-fair dependency. This finding agrees with Jerome's (1966) observations that cobalt and iron (mainly as magnetite) are "ubiquitous" in porphyry copper deposits in the pro- vinces of Arizona and Hexico. The correlation coefficient of Cu-So (-0.125) indicates that there is no relationship Votween the Cu and Sc mineralization. The negative value implies that there is b. tendency for these two elements to vary in- versely, (see Figure 8). This value.- compares with the low positive correlation coefficient of Cu-Sc in Bohol and Davao areas, Santos (1973). This situation may be reflected in the relatively lower potential for copper mineralization for the above areas, in contrast with the copper-rich Kegros area. But it must be emphasized that this difference may not be entirely due to copper mineralisation alone but also to other geochetnical parameters of the country rock. 2» Magnetic Survey The vertical magnetic intensity contour maps of the project area are shown in Figure 9» The magnetic intensity contour map of the survey area including the Camulayan area reveal«d magnetic highs over the mineralized area and magnetic lows or valley at the northern limit of the deposit. Immediately - 9 - to the north of those magnetic lows, the magnetic measurements Roem to increase gradually in tho hornblende diorito rocks. Tho inferred dip of the ore-body based on tho magnetic contour map is southwest which agrees with data obtained from drill holes. Depth-size problems do not present very much difficulties because of thi- fairly shallow magnetic source. Tho top of the orebody is commonly 50 meters from the surface. However, some ore- bodies separated by unminercalized rocks but beneath a shallower orcbody may not be adequately evaluated. The most prominent structure in the area is the northwest-southeast structure, (See Figure 2). Based on tho magnetic intensity contour expression of the area, significant tension fractures trending north-south, northeast andeeat-west may be apparent as shown in Fig. 9. Selection and isolation of significant mr-gnetic anomalies from the magnetic r.u.ps depend on several cri- teria, namely, magnetic intensity, probability of mineralization and shape of anomalous contours. It was note-d early in the work that copper-bearing rocks invariably contain abundant magnetite ranging from 1-5$ and this is reflected in areas higher than about 250 gammas. Thus, areas underlain by dacite or dioritic rocks having high magnetic readings may be considered prospective for copper mineralizations and the limits may be governed by the shape or character of the contours. Magnetic method is considered as one of the direct indicator of possible copper deposit and could be effectively used for the Basay area. However, it must be noted that there arc localized portions in the deposit which contain' very little magnetite - 10 -

B. Samar The analyzed samples were taken from the Main orebody and the Guila-guila orebody (Figure 3) • The Main orebody is approximately 1.2 km. northwest of the Guila- guila orebody. The results of the sulfide analysis for cobalt, copper, manganese, vanadium, zinc and lead are shown in Table III. It can bo observed that the range of cobalt and vanadium values are similar in the sulfides from the Main orebody and from the Guila-guila pit, except for one vanadium value (950 ppm) in the Main orebody. High copper and zinc contents are found in the Main orebody while high manganese values are localized in Guila- guila. There are more high lead values in the Main orebody, but the highest load value is found in Guila-guila. The cumulative frequency diagrams of the analyzed elements indicate that all the elements tend to have log normal distributions. The cumulative frequency curves of cobalt and zinc, copper and lead, and manganese and vanadium are shown in Figures 10, 11 and 12 respectively. The cumulative frequency diagrams of cobalt, lead and

manganese indicate the presence of two populations. Lead has an excess of low values while cobalt has an excess of high values. The background concentrations of the elements are as follows: Cu - 0.2%, Pb - 66 ppm, Co - 50 ppm, Zn - 0.01$, Mn - 31 ppm, V - 2b ppm To calculate the correlation coefficients, corre- ction clouds were constructed (Figure 13- 17). The corrélation coefficients obtained are the following: Cu/Mn » 0.19, Cu/Zn • 0.62, Cu/V - 0.6k, Cu/Co » 0.68, Cu/Pb m 0.87 These values suggest that except for CuA'n which has a low correlation coefficient copper has high moderate - 11 -

dependency with Pb, Zn, V and Co and thus these elenents may be used as possible pathfinders in the search for copper-rich kuroko deposit. These results agree with the observations of ïshikawa, et. al. (1962) that Pb, V, Zn nnd Co may bo used as guides in prospecting for kuroko deposits in Japan.

CONCLUSIONS

The Cu, Sc and Co distribution*, in the Basay, Negros Oriental copper deposit arc log-normal with an excess of low values. Fair gcochemical correlations were- observed between Cu-Co and Sc-Co while low negative or inverse correlation exists between Cu/Sc. fingnetic methods were found tc be suitable means for delineating copper mineralization in Ilegros due to the association of magnetite with copper deposits» Cobalt is not as good an indicator for copper deposits in Metros as magnetite» Lead, zinc, vanadium and cob.--.lt csn be used as trace element indicators in the search for copper-rich kuroko deposit in Sanar area. It is felt that these tmce element geochemical relationships in pyrite art also applicable in other parts of the country v/here kuroko type deposits may be found. Pyrite has proven to be a good sampling media in copper prospecting.

/sna Table I. Background and Threshold Values of Copper, Scardium and Cobalt in Core Drill Samples irou Basay, Ne.ros Oriental.

Background Threshold

Copper (%) 0.29 0.85 Scandium 57 Cobalt 18 kk

Table II. Correlation Coefficients of the Elements in Core Drill Samples from Wcfros Oriental.

Elements Correlation Coefficients

Co-Sc Q.kk Cu-Co 0.36 Cu-Sc -O.I25 Table III. Minor ttnd Trace Elements in Mineral Sulfides from Saaar Island

Sample Co Cu Mn V Zn Pb Identification ppm / ppm ppm % ppm A> Guila-guila Orebody GG-1 10 0.01 10 50 0.01 ko GG-2 10 0.01 10 Below 10 0.01 _ GG-3 15 0.01 20 10 0.1?. 55 GG-4 15 0.03 30 30 0.01 50 GG-5 20 0.01 15 30 0.01 65 GG-6 25 0.01 10 Belo?/ 10 0.05 55 GG-7 15 0.04 15 Below 10 0.0^ 35 GG-8 100 0.01 45 35 0.06 70 GG-9 4c 0.02 10 Below 10 0.03 50 GG-1O 55 Below 0. 01 10 Below 10 0.02 ko GG-11 20 0.01 60 100 0.70 65 GG-12 20 0.01 30 30 0.01 35 3P<4-13 50 0.15 20 15 _ 195 3PM-1V-A 85 0.45 290 80 0.11 ^65 SPW-18 55 0.60 220 390 1.5> 3175 SPH-18-L-2OO 25K 65 0.60 20 60 O.37 215 bPh-19-A 90 0.35 335 60 0.09 290 3PM-19-b 55 0.40 20 30 0.16 400 SPM-21 20 1.15 30 Below 10 o.ll 230 5PM-22 80 0.10 oO 80 0.05 130 SPM-23 30 2.50 200 150 0.75 255 SPH-25 185 0.40 W610 ko 0.18 185 ùtfl-?.6 60 0.35 3320 70 0.10 165 SPM-27 30 1.40 105 130 0.20 400 ÛPM-29 55 0.65 230 75 O.^fO 215 ùPM-30 55 0.50 80 20 O.VL 215 ^PM-31 50 0.60 70 50 0.14 215 JM-4 105 0.40 5^0 Below 10 0.24 445 JM-7 80 1.A-0 200 30 0.21 38O Main Orebody MO-1 20 0.40 30 Below 10 0. 0^ 65 MO-2 10 0.04 10 Below 10 0. 03 kï MÛ-3 10 0.07 10 40 0. ok 60 MÛ-4 10 0.0*+ 15 Below 10 0. 02 65 MO-5 10 0.09 15 Below 10 0. 16 k$ MO-6 10 0.03 10 Below 10 c. 01 ko 140-7 10 0.05 10 Bblo-u 10 0.,06 110 MO-8 10 Below 0.01 10 Below 10 0.,01 40 MO-9 10 0.03 10 Below 10 0.,02 50 PP-1 10 0.10 10 10 0.,01 30 PF-2 10 0.20 10 50 0..01 35 PP-3 10 0.06 2.0 95 0.,01 40 EK-1 20 0.30 35 c..2y 130 SPM-14 ko 1.90 120 ko 3..76 430 SPM-17 6G 0.65 770 100 11..25 1315 SB4-15 45 11.35 265 950 1,.95 530 SPM-16 45 8.15 75 55 1,,00 190 6PM-24 50 14.00 550 25 0,.07 110 SPM-3 105 1.35 285 160 0,.05 115 oPH-10 - - 700 375 - SPM-12 65 C+0 55 110 SPM-20 140 0.25 30 25 0,.03 90 Main Orebody Gossan MGG-1 60 O.4o 25 10 0,.03 1215 MCG-2 50 0.70 70 30 0,.02 275 MOG-3 45 0.07 60 15 0,.01 230 MOG-4 60 0.30 60 20 0,.01 1260 MGG-5 60 0.80 90 30 0,.10 1410 HOG-6 70 0.40 115 ko 0,.06 250 MOG-7 55 0.50 26o ko 0 .01 370 MOG-3 60 0.50 45 ko 0 .01 335 MOG-9 60 0.40 155 30 0 .01 925 REFERENCES

Ahrens, L.H.., Lognorual type distribution in ii.neous rock"- (V) f-d

(VI). Geochem. et Coswoc.'iiu. Acta 27, (I963) 877-890 air.' 929-938.

, G.îî., Esguerra, F.B., Kuroko-Type ore Jc-pozits in Sulat area,

Eastern S&aar, Philippines, Journal of -he Geological Society of the Philippines 28 1 (197^) 1.

Bryner, L., Geology of massive pyrite deposits v/itU special reference to the Philippines, Proc. 2nd Symp. Mineral Resources Development,

Manila (1966).

Ishikawa, A., Kt. Al., Minor elements in some altered zones of uKurol<.o" (black ore) deposits in Japan, Econ. Geol. £7 (19&2) 785.

Jerome, 3.E., Some features pertinent in exploration of porphyrjr copper deposits, in Geology of the Porphyr^ copper deposits South- western Horth America, éd. Titler, R.5. ano Hicks, L.C., The

University of Arizona Press, Tucson, Arizona, (I966) 75-85.

Kinkel, Jr. A.R., Geology of the Bacac-iv copper depo<îit^ of Marin- duque Iron Mines, S^r/iar, Copper deposits of the Philippines, Symp.

Proc. Phil. Bureau of Klines, Manila (1956) 253.

Lepeltier, C, A simplified statietic«l treat.sent of ^eochemical

data by graphical representation, TScon. Geol,, 6k (I969) 53^-550. Malicdem, D. Hinobaan porphyry ooppor depoait-Ne.-ros, Lepanto Explo- ration (Asia) Annual Technical S^iuponiuM Papers (1973) 8-17.

Prinz, 1-i., Geochemistry of Basaltic rocks: Trace elements in

...salts, vol. 1, eel, Hess, H.H. and Foldevaart, A., John ï/iley and

Sons, (1967)

Santos, G,, Reconnaissance geociiemical activation analysis survey in Northern Bohol and in Davao, Mindanao Island. Research Contract

No, 9h8, In.HA Research Contracts, 13th annual report. Tech. Reports

Series No. 111. Vienna, (1973)

Tennant, C.B. and ..'hito, M.L., Study of tl.o distribution data.

Scon. Geol. ^, (1959) 1281-90.

Williams, X.K., Statistics in the interpretation of (jeoclie^i

data, N.Z, Jour. Geol. Geophys. 10, (19b?) 771-797.

GS/lms ACKNCX.-LEDGEhENTS

We would like to express our thanks to the CDCP Mining

Corporation and Marinduque Mining and Industrial Corporation

their valuable assistance in the collection of samples.

We would like to thank Dr. L. D. Ibe, Commissioner of

PAEC, for extending his full support to the project.

Many thanks are due to pur staff, E. Herr.anuoz for the microscopic ore analysis, M. Yulo and L. Ilar.'an for their helpful cooperation. SCALE I : 1,000,000

CO 60 Km.

PANAY , 6«LF

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oUMAGUETÉ CITY

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I OVERLAPPING MMNETIC SU I OVERLAPPING MAGNETIC SURVEY FIG. 9.- VERTICAL MAGNETIC INTENSITY CONTOUR MAP OF BASAY PORPHYf INDEX MAPS OF BASAY PORPHfRY COPPER

MAP OF BASAY PORPHYRY COPPER DEPOSIT SHOWING LOCATIONS OF DIAMOND [ sEcnir 5 l SAY PORPHYRY COPPER PROSPECT, NEGROS ISLAND.

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~~FIG. 16- CORRELATION DIAGRAM OF COPPER-COBALT IN PYRITE FROM BAGACAY , SAMAR . KT —i~~

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