The Hired gold mineralization is located in the Lut Block, eastern Iran. Reduced intrusion of subvolcanic granodiorite to quartz diorite stock with porphyry texture of the post Eocene age intruded into the Eocene volcanics and pyroclastic units led to alteration and gold mineralization. Mineralization occurred as three separate parts: intrusion-hosted, proximal and distal. The Hired gold mineralization can be considered as gold mineralization related to reduced granitoid intrusions. Free gold has not been observed in the form of native gold during microscopic studies. Therefore, it appears that gold probably occurs as invisible or submicrometer-sized inclusions in sulfide minerals. Electron probe microanalysis (EPMA) confirmed the existence of sulfide minerals such as pyrrhotite, galena, pyrite and arsenopyrite having the highest gold content; however, because of the relative abundance of pyrite and arsenopyrite, a high gold concentration corresponds to the presence of these sulfides. Considering the paragenetic sequences, gold mineralization occurred as invisible gold in the early and late hydrothermal stages.

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Garnet porphyroblasts contained in the garnet-sillimanite gneiss from the Lützow-Holm Complex at Skallevikshalsen, East Antarctica, have a phosphorus-poor core and phosphorus-rich rim. The core/rim boundary of the phosphorus zoning is discontinuous. The irregular shape of this core/rim boundary together with the pressure difference between the core and the rim inferred from the difference in aluminosilicate inclusions (kyanite in the core and sillimanite in the rim) suggests that this is the resorption/reprecipitation boundary. The difference between phosphorus concentrations in the garnet core and rim is accompanied by a change in phosphate inclusions in the garnet. Apatite and monazite are included in the phosphorus-poor garnet core, whereas monazite alone is included in the phosphorus-rich garnet rim. Utilizing the core/rim boundary as a contemporaneous surface when comparing different garnet grains, the timing of the discontinuous phosphorus-zoning formation (and thus, the garnet resorption) and change in the phosphate assemblage can be correlated to the pressure-temperature path of the garnet-sillimanite gneiss. The phosphorus-poor core of the garnet mainly formed during the prograde stage in the kyanite to sillimanite stability fields under which apatite probably buffered the phosphorus-content of garnet, and the phosphorus-rich garnet rim possibly crystallized from the melt at the retrograde stage near the vapor saturated solidus under which monazite alone (without apatite) probably did not buffer the phosphorus-content of garnet. Garnet resorption occurred during the decompression stage between these two garnet growth stages.

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The crystal structure of a chromian pumpellyite K_0.03Na_0.07Ca_7.82Mn²⁺_0.01Mg_1.95Fe³⁺_0.05V³⁺_0.01Cr³⁺_3.77Al_6.52Ti_0.02Si_11.82O_42.06(OH)_13.94 (Z = 1) from Sarany in the Russian Urals was studied using optical spectroscopy and single-crystal X-ray diffraction methods. Five discrete peaks were observed in an optical spectrum. Of these, three at 392(υ₂), 574(υ₁) and 726 nm were attributed to Cr³⁺; one at 456 nm to Fe³⁺; and a peak at 291 nm is related to M-O charge transfer. The crystal field parameters determined here (B, C and 10Dq) give 94% ionic character of Cr-O bonds and a mean ^VIM-O distance of 1.954 Å. The crystal structure of chromian pumpellyite with a = 8.809(3), b = 5.9330(9), c = 19.137(1) Å, β = 97.606(2)° at 90 K, and a = 8.807(6), b = 5.943(4), c = 19.18(1) Å, β = 97.44(2)° at 293 K was refined using 1297 unique reflections measured at 90 K, converging at R = 2.3%. Site occupancies of the main constituent elements at the two independent octahedral X and Y sites are X = 0.49Mg + 0.308Cr + 0.202Al and Y = 0.742Al + 0.258Cr. Although Cr³⁺ ions occupy both the X and Y sites, the site preference of chromium for the X site is stronger than that for the Y site, as indicated by the distribution coefficient of chromium between the X and Y sites, K_D = (Cr/Al)_X/(Cr/Al)_Y, of 4.39. The substitution of Cr³⁺ for Al in the Y site directly results in structural changes, whereas that in the X site is not effective for structural change.

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To determine the petrographic contrasts between ilmenite- and magnetite-series magmas, we assessed the rock descriptions, modal compositions, and whole-rock chemical compositions for ilmenite- and magnetite-series gabbroic masses in the Ryoke and San-in belts and focused on the primitive phases of the two plutonic belts. We obtained the following results:
     (1) The San-in gabbroids contain variable modal amounts of magnetite, up to 5.8%, whereas no magnetite was detected in the Ryoke gabbroids. The outcrop measurements of magnetic susceptibility exhibited good positive correlation with the magnetite contents of the outcrop samples.
     (2) As compared to the San-in gabbroids, the Ryoke gabbroids are generally less abundant in alteration minerals such as chlorite and fibrous actinolite and more abundant in olivine- and orthopyroxene-bearing phases.
     (3) The rock texture and whole-rock chemical compositions indicate that the Ryoke gabbroids have more cumulative characteristics than the San-in gabbroids. The compositional differences between them can be mainly explained by the differences between their degrees of crystal accumulation.
     (4) We were unable to detect any significant differences between the N-MORB normalized patterns of trace-elements and REEs in the Ryoke and San-in gabbroids.
     Features (2) and (3) may be responsible for the differences between the emplacement depths of the Ryoke and San-in gabbroic masses, although these features are independent of redox states. Feature (4) suggests that the two gabbroids have a common petrogenetic background.
     Based on these results, we conclude that the contamination of Ryoke gabbroic magma by sediments is insignificant, having little or no effect on redox states. It is more likely that the divergent redox states of the two gabbroic magmas are primarily attributable to the differences in the volatile components involved in the f_O2 buffer reactions.

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Nantai volcano, northeast Japan, is a stratovolcano whose recent eruptive activity is poorly known. This paper presents the characteristics and ages of a newly discovered Holocene succession of volcanic and sedimentary units exposed at the northern sector of the present summit crater of Nantai volcano. The stratigraphic relationships and three accelerator mass spectrometry (AMS) ¹⁴C ages for eruptive products and lacustrine deposits of the northern sector of the summit crater show that Nantai volcano was active after the 15-14 cal ka BP eruption, which was thought to be the latest eruption of the volcano. After the 15-14 cal ka BP eruption, the summit crater was filled by a lake in which a water-chilled volcanic and tuff breccias (Goshinbutsunagi Volcanic Breccia) and the overlying lacustrine deposit (Nantai Lacustrine Deposit 1: NLD1) were emplaced. The ¹⁴C age of ∼ 8 cal ka BP obtained from a wood fragment in the bottom of NLD1 defines the initiation of the deposition of NLD1 in the crater lake. The crater lake dried up before 7 cal ka BP, following which a phreatomagmatic eruption occurred in the summit cater, forming Nantai-Yudonoyama Tephra (NYT). NYT is the latest recognized eruption product of Nantai volcano, and it underlies the second lacustrine deposit (Nantai Lacustrine Deposit 2) formed in the renewed crater lake. The young age of 7 cal ka BP obtained from the two charred wood stumps in NYT highlights that Nantai is an active volcano.

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Edited by the Abstracting Committee, Japan Association of Mineralogical Sciences

Age Determination 105038—105050;
Rock-Forming Minerals and Petrology 105051—104065

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