『Abstract
　Recent fluvial sediments of the Rio Neuquen（後ろのeの頭に´）, Argentina, contain variable amounts of placer gold. In addition to rounded, detrital placer gold, the sediments also contain pristine crystalline gold (type 1 gold), which occurs as overgrowths on detrital placer gold cores. Type 1 gold is locally rimmed by gold with a wormlike or crystalline texture (type 2 gold). The chemistry of the primary cores indicates variable intragrain and intergrain compositional heterogeneity. This is interpreted to indicate a multisource origin. Type 1 gold is composed of virtually pure gold (＞98 at.％ Au) and type 2 gold is an Au-Hg amalgam (4-9 at.％ Hg). Both varieties are authigenic in origin.
　The formation of the virtually pure type 1 gold is interpreted to be due to the addition of Au from an external source, rather than by the removal of Ag and other metals. The AuHgAg type 2 gold is interpreted to be due to Hg contamination from historic mining. Type 1 gold is interpreted to be analogous to the Ag-poor rims present on many placer gold grains. The evidence presented in this study supports the view that the Ag-poor rims on placer gold grains are the result of Au addition and not Ag removal. This study also has implications for both quantitative morphological and paragenetic studies of placer gold grains.』

Introduction
Location and regional geology
Primary gold deposits in the area
Fluvial system
Methodology
Crystalline grain morphology
Chemistry
　Grain cores
　Crystalline gold
Origin of the gold types
Formation of crystalline gold in the Neuquen（後ろのeの頭に´） system
　Loss of Ag
　Internally sourced Au
　Externally sourced Au
　Bacterially mediated Au precipitation
　Colloidal and humic sources of Au
　Role of mercury
　Summary of gold formation
Analogies and implications
Conclusions
Acknowledgments
References

【銀に乏しい縁をもつ金粒子の成因】
（１）Agは取り去られたという説：

• Desborough,G.A.(1970): Silver depletion indicated by microanalysis of gold from placer occurrences, Western United States. Economic Geology, 65, 304-311.
• Giusti,L. and Smith,D.G.W.(1984): An electron microprobe study of some Alberta placer gold. Tschermaks Mineralogische und Petrographische Mitteilungen, 33, 187-202.
• Michailidis,K.(1989): Gold geochemistry from the Gaillikos River placer deposits, central Macedonia, Greece. Chemie der Erde, 49, 95-103.
• DiLabio,R.N.W.(1990): Classification and interpretation of the shapes and surface textures of gold grains from till on the Canadian shield: Current research 1990, part C. Geological Survey of Canada, Paper 90-1c, 323-329.
• Knight,J. and McTaggart,K.C.(1990): Lode and placer gold of the Coquihalla and Wells areas, British Columbia, (92H, 93H). British Columbia Department of Mines, Exploration in British Colimbia, no. 1089, 105-118.
• Herail（eの頭に´）,G., Fornari,M., Viscarra,G. and Miranda,V.(1990): Morphological and chemical evolution of gold grains during the formation of a polygenetic fluviatile placer: The Mio-Pleistocene Tipuani placer example (Andes, Bolivia). Chronique de la Recherche Miniere, 500, 41-49.
• Krupp,R.E. and Weiser,T.(1992): On the stability of gold-silver alloys in the weathering environment. Mineralium Deposita, 27, 268-275.
• Knight,J.B., Morison,S.R. and Mortensen,J.K.(1999a): Relationship between placer gold shape, rimming, and distance of fluvial transport as exemplified by gold from the Klondike district, Yukon Territory, Canada. Economic Geology, 94, 635-648.
• Knight,J.B., Mortensen,J.K. and Morison,S.R.(1999b): Lode and placer gold composition in the Klondike district, Yukon Territory, Canada: Implications for the nature and genesis of Klondike lode and placer gold. Economic Geology, 94, 649-664.

（２）縁は金がつけ加わったという説：

• Bowdish,F.W.(1983): Fire assaying for gold and silver. Nevada Institute of Technology, International Gold/Silver Conference III, Reno, Nevada, Proceedings.
• Mann,A.W.(1984): Mobility of gold and silver in lateritic weathering profiles: Some observations from Western Australia. Economic Geology, 79, 38-49.
• Stoffregen,R.(1986): Observations on the behaviour of gold during supergene oxidation at Summitville, Colorado, USA, and implications for electrum stability in the weathering environment. Applied Geochemistry, 1, 549-558.
• Bowles,J.F.W.(1988): Mechanical and chemical modification of alluvial gold. Bulletin and Proceeding of the Australian Institute of Mining and Metallurgy, 293, 9-11.
• Groen,J.C., Craig,J.R. and Rimstidt,J.D.(1990): The gold-rich formation on electrum grains in placers. Canadian Mineralogist, 28, 207-228.
• Bowell,R.J.(1992): Supergene gold mineralogy at Ashanti, Ghana: Implications for the supergene behaviour of gold. Mineralogical Magazine, 56, 545-560.
• Craw,D.(1992): Growth of alluvial gold particles by chemical accretion and reprecipitation, Waimumu, New Zealand. New Zealand Journal of Geology and Geophysics, 35, 157-164.
• Santosh,M., Philip,R., Jacob,M.K. and Omana,P.K.(1992): Highly pure placer gold formation in the Nilambur Valley, Wynad gold field, southern India. Mineralium Deposita, 27, 336-339.
• Southam,G.(1998): Quantification of sulfur and phosphorus within secondary gold rims on Yukon placer gold. Geology, 26, 339-343.
• 本論文

（３）上記のどちらもあるという説：

• Loen,J.S.(1994): Origin of placer buggets and history of formation of glacial gold placers, Gold Creek, Granite County, Montana. Economic Geology, 89, 91-104.
• Youngson,J.H. and Craw,D.(1995): Evolution of placer gold deposits during regional uplift, Central Otago, New Zealand. Economic Geology, 90, 731-745.