ISSN 1028334X, Doklady Earth Sciences, 2014, Vol. 458, Part 2, pp. 1230–1235. © Pleiades Publishing, Ltd., 2014. Original Russian Text © A.A. Sorokin, A.V. Ponomarchuk, A.V. Travin, V.A. Ponomarchuk, K.D. Vakhtomin, 2014, published in Doklady Akademii Nauk, 2014, Vol. 458, No. 4, pp. 452–458.
GEOCHEMISTRY
New 40Ar/39Ar Age of Granitic Rocks and Related Gold Mineralization at the Kirovskoye Deposit (Southeastern Margin of the North Asian Craton) A. A. Sorokina, A. V. Ponomarchukb, A. V. Travinb, c, V. A. Ponomarchukb, and K. D. Vakhtomin† a Presented by Academician V.G. Moiseenko April 20, 2014 Received April 29, 2014
Abstract—The Kirovskoye gold deposit located in the southern part of the Selenga–Stanovoi superterrane at the southeastern margin of the Siberian craton is one of the largest ore deposits in the eastern regions of the Russian Far East. 40Ar/39Ar geochronological studies revealed that the age of the quartz–diorite–porphyrite and granodiorite–porphyry dikes is 128–126 Ma. This estimate agrees with the previous U–Pb age of 125 ± 2 Ma for the Dzhalinda granodiorites. The age of hydrothermal oreforming processes was estimated at ~121–120 Ma. These results allow us to infer that a relationship between Kirovskoye gold mineralization was formed as a result of postmagmatic hydrothermal activity, which accompanied the emplacement of the Dzhalinda intrusion and coeval dikes. DOI: 10.1134/S1028334X14100134
The southeastern margin of the North Asian craton hosts a variety of mineral deposits and occurrences of nonferrous, rare, and precious metals (e.g., Okhok, Bamskoye, Berezitovoye, Vykhodnoye, Kirovskoye, Mogotinskoye, Dess, Nakhodka, Apsakan, Chilchin skoye, Ledyanoye, Atugey, Serebryanii Klyuch, etc.) [1] and others. These ore deposits belong to the Meso zoic metallogenic epoch. In recent years there has been growing interest in understanding the precise chronology of the formation of the bedrock and impor tant marker horizons of ore mineralization, which could help to establish relationships between mineral ization, magmatic complexes, and tectonic events ([2– 10] and others). The results of such studies can provide the necessary information for metallogenic modeling. The Kirovskoye gold deposit is a good example of one of such targets. It is located in the southern part of the Selenga–Stanovoi superterrane at the eastern margin of the Siberian craton (Fig. 1) and was discov ered at the head of a rich placer on the Dzhalinda River in the late 19th century and operated intermit tently through 1962 ([1] and others). This deposit still † Deceased. a Institute of Geology and Management of Natural Resources,
Far East Branch, Russian Academy of Sciences, Blagoveshchensk, Russia b Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia c Tomsk State University, Tomsk, Russia email:
[email protected]
attracts considerable interest as a large placer mining target. The deposit extends approximately east–west and is bound to the endo and exocontacts of the Dzhal inda granitic intrusion [11], which constitutes part of the Early Cretaceous Burinda complex (Fig. 1). The intrusion is composed of two phases, the early quartz monzodiorite and diorite in the southwest and the late granodiorite, granodiorite–porphyry in the center, as well as a series of late granodiorite porphyry and quartz diorite porphyrite dikes and sills [11]. The studied intrusion cuts through the metamor phic and magmatic rocks of the Selenga–Stanovoi superterranes and Jurassic terrigenous rocks of the Strelka depression (Fig. 1). The ore bodies are con fined to hydrothermally altered granitic rocks in the southern part of the intrusion and sedimentary rocks of the Strelka depression. Mineralization occurs in quartzsulfide veins, up to 670 m long and 1.5 m thick, which are typically milky white quartz with dissemi nated arsenopyrite, chalcopyrite, bismuthite, pyrite, sphalerite, tetradymite, scheelite, pyrrhotite, rare native bismuth, gray copper ore, enargite, and gold. Depending on their sulfide content, all ores are classi fied as low and moderately sulfide ores [11]. The available isotopic age determinations from the Dzhalinda intrusion and wallrock metasomatites vary widely. For example, the K–Ar age of granitic rocks was determined as 110–140 Ma (see the review in [1, 5]), and the ages of wallrock metasomatites were estimated at 105 Ma (K–Ar method) and 131–126 Ma (Rb–Sr method) [5]. The most reliable age (125 ± 2 Ma, U–Pb method) was obtained for latephase grano
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1231
124°30′
126° 114°
56° 52°
48°
54°20′
2 km 1
124°15′ 2
3
124°15′ 4
5
6
7
8
9
10
Fig. 1. Location of the Kirovskoye gold deposit within the tectonic framework of eastern Asia, modified after [11]. 1—Paleozoic volcanic and volcanoterrigenous rocks of the Mongolia–Okhotsk fold belt; 2—Middle–Upper Jurassic coarse clastic rocks of the Strelka depression; 3—presumably Early Precambrian metamorphic rocks of the southeastern margin of the North Asian cra ton; 4—Middle Jurassic diorites, quartz diorites, and granodiorites; 5—Middle–Late Jurassic pyroxenites, peridotites, gabbros, and gabbro–diorites; 6—Early Cretaceous quartz monzodiorites and diorites, granodiorites, and granites of the Dzhalinda intru sion; 7—quartz–diorite–porphirite and granodiorite–porphyry dikes; 8—Cenozoic unconsolidated deposits; 9—locations of samples collected for geochronological studies. The hatched area denotes the MongoliaOkhotsk fold belt, and the Kirovskoye deposit is shown by a star on the inset.
diorites in the central part of the Dzhalinda intrusion [11]. At the same time, the age of dikes, which are abundant within the deposit (Fig. 1), is unknown. Using the available data, the age of magmatism and oreforming events can be estimated tentatively as Early Cretaceous (≈140–105 Ma), which is insuffi cient for establishing a reliable temporal relationship between the processes of interest and requires further investigation. 40Ar/39Ar
geochronological studies on wallrock metasomatites and magmatic rocks developed within the mineralized zone (sampling locations are shown in Fig. 1) were conducted at the Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, to elucidate the relationship between the magmatism and hydrothermal activity. For 40Ar/39Ar dating, mineral separates were handpicked under a binocular microscope from the 0.25–0.15 mm frac tions of the crushed rock sample. The samples were DOKLADY EARTH SCIENCES
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irradiated in a VVRK cadmiumlined research reac tor at the Research Institute of Nuclear Physics (Tomsk). The neutron flux gradient was no greater than 0.5% across the gage volume of the sample. Typ ical 40Ar blank values of 5 × 10–10 ncm3 were achieved at 1200°C for 10 min. Argon was purified using SAES Ti and Zr–Al getters. The argon isotopic composition was measured with a Micromass Noble Gas 5400 mass spectrometer (UK). The correction factors derived for 36, 37, 40Ar isotopes derived from Ca and K were (39Ar/37Ar)Ca = 0.00073 ± 0.000026, (36Ar/37Ar)Ca = 0.00032 ± 0.000021, (40Ar/39Ar)K = 0.0641 ± 0.0001. The mass discrimination factor was monitored by measuring a batch of purified atmospheric argon. The mean 40Ar/36Ar was 296.5 ± 0.5 during measurements. The samples of hydrothermal wallrock sericite– feldspar–quartz metasomatites (VK10 and VK31) (Fig. 1) for geochronological studies were collected in adit 16, where they host the highest grade vein no. 232.
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SOROKIN et al. Age, Ma 120
128 ± 2 Ma Sample VK6 (amphibole)
80 120
126 ± 2 Ma Sample VK6 (biotite)
40 80 120 0
127 ± 1 Ma Sample VK9 (biotite)
40 80 0 40
0
20
40
60
100 80 %39Ar released
Fig. 2. Plots of stepwise heating of amphibole and biotite from the quartz–diorite–porphyrite dike (sample VK6), and biotite from the quartz–diorite–porphyrite dike (sample VK9). The errors are quoted at +2σ.
Age, Ma 140 121 ± 2 Ma Sample VK17 (sericite)
100 60
140 120 ± 2 Ma Sample VK17 (feldspar)
100 20 0
60
20 0
20
40
60
80 100 %39Ar released
Fig. 3. Plots of stepwise heating of sericite and seritized feldspar from the hydrothermally altered granodiorite–porphyry dike (sample VK17).
Because a reliable age is available for granodiorites from the central part of the Dzhalinda intrusion [11], the goal of this study is to provide a highprecision age estimate for dikes near the intrusive contacts. The samples for geochronological studies were collected
from two quartz–diorite–porphyrite dikes (VK6 and VK9) and one granodiorite–porphyry dike (VK17) at the southern exocontact of the intrusion (Fig. 1). The geochronological results presented in the table and in Figs. 2–4 can be summarized as follows: DOKLADY EARTH SCIENCES
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40Ar/39Ar
stepwise heating results for mineral separates from hydrothermally altered wallrock metasomatites and granitic rocks within the Kirovskoye ore deposit Step
1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 1 2 3 4 5 6
T, °C
%39Ar released
40
Ar/39Ar
37
Ar/39Ar
36
Ar/39Ar
Age, Ma
550 650 750 850 950 1050 1130
Sample VK6 (amphibole), J = 0.005407 ± 0.000076 3.0 20.64 ± 0.03 0.91 ± 0.77 0.043 ± 0.001 10.8 19.24 ± 0.01 1.16 ± 0.30 0.0185 ± 0.0004 19.9 16.702 ± 0.014 0.18 ± 0.18 0.0098 ± 0.0008 26.3 17.49 ± 0.01 0.53 ± 0.38 0.0130 ± 0.0008 41.0 16.35 ± 0.01 2.28 ± 0.24 0.0084 ± 0.0005 79.3 14.61 ± 0.01 2.73 ± 0.06 0.0043 ± 0.0002 100.0 14.69 ± 0.01 4.5 ± 0.03 0.0043 ± 0.0003
75.2 ± 4.9 129.6 ± 2.1 130.0 ± 2.8 128.4 ± 2.7 130.6 ± 2.2 125.7 ± 1.8 126.3 ± 1.9
500 625 725 825 925 1025 1075 1130
Sample VK6 (biotite), J = 0.005453 ± 0.000077 0.4 26.73 ± 0.19 0.017 ± 0.009 0.0506 ± 0.0046 4.6 30.25 ± 0.02 0.001 ± 0.001 0.0602 ± 0.0006 27.5 18.549 ± 0.008 0.001 ± 0.001 0.0178 ± 0.0001 38.4 15.857 ± 0.007 0.001 ± 0.001 0.0090 ± 0.0003 45.0 14.992 ± 0.006 0.001 ± 0.001 0.0046 ± 0.0004 61.3 14.200 ± 0.006 0.001 ± 0.001 0.0026 ± 0.0001 74.2 13.653 ± 0.007 0.001 ± 0.001 0.0017 ± 0.0001 100.0 14.409 ± 0.005 0.001 ± 0.001 0.0038 ± 0.0001
112.3 ± 12.8 118.5 ± 2.3 126.1 ± 1.8 125.4 ± 1.9 129.3 ± 2.1 127.4 ± 1.8 125.1 ± 1.7 126.1 ± 1.7
VK9 (biotite), J = 0.003229 ± 0.000027 89.4 ± 1.4 0.014 ± 0.014 44.94 ± 0.13 0.003 ± 0.003 27.017 ± 0.018 0.0005 ± 0.0005 24.748 ± 0.009 0.0008 ± 0.0003 24.706 ± 0.010 0.0015 ± 0.0002 25.352 ± 0.016 0.0003 ± 0.0003 23.575 ± 0.008 0.0001 ± 0.0001
0.267 ± 0.009 0.100 ± 0.002 0.0154 ± 0.0007 0.0080 ± 0.0003 0.0062 ± 0.0004 0.0083 ± 0.0001 0.0039 ± 0.0001
59.2 ± 13.9 87.6 ± 3.8 126.4 ± 1.5 125.9 ± 1.2 128.5 ± 1.2 128.6 ± 1.0 126.2 ± 1.0
500 600 700 800 900 1010 1130
0.3 2.0 12.0 33.9 44.9 59.3 100.0
500 600 700 800 900 1000 1065 1130
Sample VK17 (sericite), J = 0.005143 ± 0.000069 1.3 35.8 ± 0.1 0.004 ± 0.003 0.062 ± 0.003 8.5 16.943 ± 0.008 0.001 ± 0.001 0.0135 ± 0.0006 21.8 14.605 ± 0.006 0.001 ± 0.001 0.0037 ± 0.0003 33.6 14.611 ± 0.007 0.001 ± 0.001 0.0038 ± 0.0003 48.9 14.548 ± 0.008 0.0015 ± 0.0006 0.0035 ± 0.0002 70.6 15.446 ± 0.006 0.001 ± 0.001 0.0054 ± 0.0001 87.0 14.828 ± 0.006 0.001 ± 0.001 0.0036 ± 0.0003 100.0 15.119 ± 0.009 0.0007 ± 0.0005 0.0051 ± 0.0002
153.1 ± 8.9 116.3 ± 2.1 121.2 ± 1.7 121.0 ± 1.8 121.2 ± 1.6 124.2 ± 1.6 123.3 ± 1.8 122.0 ± 1.7
500 650 800 900 1015 1130
Sample VK17 (feldspar), J = 0.00504 ± 0.000066 2.1 36.5 ± 0.4 0.02 ± 0.01 0.099 ± 0.007 16.7 16.35 ± 0.03 0.001 ± 0.001 0.010 ± 0.001 44.2 14.87 ± 0.01 0.002 ± 0.001 0.0043 ± 0.0005 69.2 14.74 ± 0.01 0.001 ± 0.001 0.0041 ± 0.0005 84.3 14.89 ± 0.02 0.001 ± 0.001 0.004 ± 0.001 100 15.02 ± 0.02 0.005 ± 0.001 0.004 ± 0.001
64.8 ± 18.2 116.7 ± 3.9 119.5 ± 2.0 119.3 ± 1.9 119.2 ± 3.6 120.6 ± 3.5
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Table. (Contd.) %39Ar released
40Ar/39Ar
37Ar/39Ar
36Ar/39Ar
Step
T, °C
1 2 3 4 5 6 7 8 9 10 11
500 575 625 675 725 775 825 900 975 1050 1130
Sample VK10 (sericite), J = 0.004704 ± 0.000058 6.4 19.658 ± 0.009 0.15 ± 0.06 0.0056 ± 0.0002 19.8 17.292 ± 0.008 0.14 ± 0.03 0.0021 ± 0.0002 28.5 16.222 ± 0.006 0.69 ± 0.07 0.0030 ± 0.0002 38.5 15.637 ± 0.006 2.02 ± 0.03 0.0024 ± 0.0002 48.8 15.522 ± 0.006 0.25 ± 0.03 0.0026 ± 0.0002 57.2 15.550 ± 0.006 0.01 ± 0.01 0.0037 ± 0.0002 66.1 15.227 ± 0.005 0.05 ± 0.04 0.0030 ± 0.0002 76.2 15.138 ± 0.007 0.01 ± 0.01 0.0022 ± 0.0003 88.3 14.928 ± 0.007 0.09 ± 0.01 0.0021 ± 0.0002 95.8 15.314 ± 0.008 0.01 ± 0.01 0.0021 ± 0.0004 100.0 15.623 ± 0.005 0.01 ± 0.01 0.0029 ± 0.0002
146.7 ± 1.8 136.2 ± 1.7 125.2 ± 1.5 122.5 ± 1.5 121.1 ± 1.5 118.7 ± 1.5 117.8 ± 1.5 118.9 ± 1.6 117.6 ± 1.4 120.5 ± 1.7 121.2 ± 1.5
500 600 700 800 900 1000 1130
Sample VK31 (adularia), J = 0.004899 ± 0.000063 5.2 22.18 ± 0.02 0.0005 ± 0.0003 0.0135 ± 0.0006 21.1 17.869 ± 0.009 0.0002 ± 0.0001 0.0071 ± 0.0002 43.7 15.101 ± 0.005 0.0001 ± 0.0001 0.0017 ± 0.0001 61.7 14.671 ± 0.006 0.0001 ± 0.0001 0.0029 ± 0.0001 73.1 14.679 ± 0.007 0.0002 ± 0.0002 0.0027 ± 0.0003 84.5 15.359 ± 0.006 0.0004 ± 0.0003 0.0039 ± 0.0001 100 15.276 ± 0.006 0.0002 ± 0.0001 0.0043 ± 0.0002
154.1 ± 2.4 134.3 ± 1.7 124.5 ± 1.6 118.1 ± 1.5 118.7 ± 1.6 121.4 ± 1.5 119.7 ± 1.5
1 2 3 4 5 6 7
Age, Ma
T—temperature, error ±1°C, J—Jvalue, parameter characterizing the neutron flux.
(1) The quartz–diorite–porphyrite dike (sample VK6) yielded an amphibole age of 128 ± 2 Ma (97% 39Ar release on plateau) and a biotite age of 126 ± 2 Ma (95% 39Ar release on plateau). (2) The quartz–diorite–porphyrite dike (sample VK9) yielded a biotite age of 127 ± 1 Ma (98% 39Ar release on plateau). (3) The age obtained on partly chloritized biotite from the hydrothermally altered granodiorite–por phyry dike (sample VK17) is 121 ± 2 Ma (91% 39Ar release on plateau). (4) The age obtained on sericite from the wallrock metasomatites (sample VK10) is 120 ± 1 Ma (72% 39Ar release on plateau). (5) The age obtained on adularia from the wallrock metasomatites (sample VK31) is 120 ± 2 Ma (79% 39Ar release on plateau). These results suggest that both quartz–diorite– porphyrite and granodiorite–porphyry dikes from the Kirovskoye gold deposit fall in the age range 128– 126 Ma, which corresponds to a recent U–Pb age of 125 ± 2 Ma for granodiorites from the Dzhalinda intrusion [11]. Based on these data, the age of hydro thermal oreforming events can be estimated at 121– 120 Ma. This suggests that the Kirovskoye gold miner alization was formed as a result of postmagmatic hydrothermal activity, which accompanied the
emplacement of the Dzhalinda intrusion and coeval dikes. In addition, our results allow us to infer a relation ship between the magmatism and oreforming pro cesses at the southeastern margin of the North Asian craton. For example, the age of granitic rocks from the Dzhalinda intrusion is almost identical to a recent age estimate (127–122 Ma) obtained for a series of massifs within the Tynda–Bakaran complex [9, 12]. There fore, they are older than the magmatic rocks that have been emplaced within these superterranes during the final stages of Late Mesozoic magmatic activity at 117–93 Ma [12–14]. Interestingly, ore formation within the Kirovskoye gold deposit took place earlier (~120 Ma) than ore forming processes at other localities along the south eastern margin of the North Asian craton. For exam ple, two stages of gold–polymetallic mineralization occurred at the Berezitovoye deposit: at 132–131 and ≈125 Ma [7, 8]. The age of gold–silver (Dess occur rence) and silver–polymetallic mineralization (Mog otinskoye deposit) is 129–125 Ma [2–4]. Finally, the age of hydrothermal alteration, which accompanied Mo mineralization at the Vykhodnoye occurrence, is 125–122 Ma [9]. A similar age estimate (123– 122 Ma) was obtained for the Borgulikan porphyry DOKLADY EARTH SCIENCES
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Age, Ma 140 120 ± 1 Ma Sample VK10 (sericite)
100 60
140 120 ± 2 Ma Sample VK31 (adularia)
100 20 0
60 20 20
0
40
60
80 100 %39Ar released
Fig. 4. Plots of stepwise heating of sericite (sample VK10) and adularia (sample VK31) from wallrock metasomatites.
Mo–Cu–(Au) mineralization [15] located in the east ern part of the Argun terrane. ACKNOWLEDGMENTS This study was supported by the Russian Founda tion for Basic Research (project no. 140500734), the Presidium of the Far East Branch of the Russian Acad emy of Sciences (projects nos. 12I0ONZ01, 12 IISO08030), and the Ministry of Education and Science of the Russian Federation. REFERENCES 1. L. V. Eirish, Metallogeny of Gold in Amur River Area (Amur Oblast, Russia) (Dal’nauka, Vladivostok, 2002) [in Russian]. 2. I. V. Buchko, A. A. Sorokin, V. A. Ponomarchuk, et al., Dokl. Akad. Nauk 435 (4), 506–509 (2010). 3. I. V. Buchko, A. A. Sorokin, V. A. Ponomarchuk, et al., Tikhookean. Geol. 31 (2), 69–74 (2012). 4. I. V. Buchko, Ir. V. Buchko, A. A. Sorokin, et al., Geologiya Rud. Mestorozhd. 56 (2), 118–130 (2014). 5. V. G. Moiseenko, V. A. Stepanov, and Yu. P. Shergina, Dokl. Akad. Nauk 369 (3), 354–356 (1999).
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6. V. Yu. Prokof’ev, I. A. Baksheev, L. D. Zorina, et al., Dokl. Akad. Nauk 409 (5), 673–676 (2006). 7. A. A. Sorokin, A. V. Mel’nikov, V. A. Ponomarchuk, et al., Dokl. Akad. Nauk 421 (1), 86–89 (2008). 8. A. A. Sorokin, V. A. Ponomarchuk, A. V. Travin, et al., Geol. Geofiz. 55 (3), 335–348 (2014). 9. V. I. Sotnikov, A. A. Sorokin, V. A. Ponomarchuk, et al., Dokl. Akad. Nauk 416 (6), 794–798 (2007). 10. I. V. Chernyshev, A. V. Chugaev, V. Yu. Prokof’ev, et al., in Materials of the 5th Russian Conference on Isotope Geochronology (IGEM RAN, Moscow, 2012), pp. 364– 366 [in Russian]. 11. V. V. Koshelenko, The State Geological Map of the Russian Federation, Stanovaya Series, 2nd. ed., Sheet N51XVII (VSEGEI, St. Petersburg, 2011) [in Russian]. 12. A. M. Larin, A. B. Kotov, E. B. Sal’nikova, et al., Dokl. Akad. Nauk 456 (3), 314–319 (2014). 13. A. A. Sorokin, A. P. Sorokin, V. A. Ponomarchuk, et al., Dokl. Akad. Nauk 451 (5), 560–564 (2013). 14. A. A. Sorokin, A. P. Sorokin, V. A. Ponomarchuk, et al., Dokl. Akad. Nauk 445 (4), 445–449 (2012). 15. V. I. Sotnikov, A. A. Sorokin, V. A. Ponomarchuk, et al., Geol. Geofiz. 48 (2), 229–237 (2007).
Translated by N. Kravets
