Halloysite is a common pedogenic clay mineral, often found in young soils developed on volcanic deposits (Dixon, 1989), It is a member of the kaolin group of clays with the same ideal stoichiometric composition as kaolinite [Al2Si2O5(OH)4]. Halloysite, however, often contains water of hydration (i,e., Al2Si2O5(OH)4·nH2O), and is commonly found with a tubular morphology, This “rolling” of halloysite has received a great deal of study because there is no generally agreed upon mechanism for the process and there is no corresponding phenomenon in natural kaolinite (e.g. , Bates et al., 1950; Bailey, 1989; Singh, 1996; Singh and Mackinnon, 1996). The crystal structure of halloysite often shows stacking disorder. This property, combined with a rolled morphology, makes identification by X-ray diffraction (XRD) difficult. The XRD peaks at 7.5, 4.4, and 3.6 Å are often asymmetric with a large width at half peak height (Bailey, 1989).

The residual kaolin deposits near Lastarria, South-Central Chile, were formed by weathering of subvolcanic quartz porphyry stocks, which intruded the metamorphic basement of the Coastal Cordillera. The clay fractions (<2 µm) consist mainly of poorly-ordered, very fine-grained kaolinite and lath-shaped illite (17–38 wt. %) with minor amounts of quartz, sanidine, and goethite. A sample from the top of the deposit contains major quantities of gibbsite morphologically indistinguishable from kaolinite flakes. The gibbsite-free clays contain 35.5–36.6 wt. % Al2O3, 0.4–2.6 wt. % Fe2O3, 1.3–3.9 wt. % K2O, and have low TiO2 concentrations (<0.02 wt. %). The absence of quartz veining, the abundance of melt inclusions, and the scarcity of secondary fluid inclusions in quartz phenocrysts from altered rocks imply a lack of significant hydrothermal activity in the quartz porphyries. The δ 18O and δD values of the kaolins indicate formation in a weathering environment at significantly higher annual mean air temperatures (∼12°C) than present mean temperatures of ∼9.4°C. Uplift of the region alone probably cannot account for the change in climate. The stable isotope composition of gibbsite is consistent with an origin of desilication of kaolinite at superficial temperatures. Various criteria proposed to distinguish supergene from hypogene kaolins are discussed.

In situ thermal recovery methods such as cyclic steam stimulation (CSS) are required to extract highly viscous bitumen from the Clearwater Formation oil sands of Alberta, Canada. The injection of hot fluids during CSS has altered the mineralogy of the sands, resulting in the loss of some minerals (e.g. disseminated siderite, volcanic glass) and precipitation of others (e.g. zeolites and abundant hydroxy-interlayered smectite). The high temperatures and high water—rock ratios associated with CSS might also alter the oxygen and hydrogen isotopic compositions of pre-existing clay minerals even in the absence of mineralogical changes. The present study exploits this fact to track the movement of injected hot fluids during CSS. Berthierine, a common diagenetic clay mineral in the Clearwater sands, survived CSS but acquired substantially lower δ18O and δ2H values in cores located ≤ 10 m from the injection well. In contrast, the oxygen and hydrogen isotopic compositions of berthierine in cores located further from the injection well were generally unaffected, except at the depth of steam injection where horizontal fractures facilitate greater lateral penetration of hot fluids. Smectitic clays in near-injector cores also acquired lower δ18O values during CSS, but a systematic shift in δ2H values was not observed. While hydrogen-isotope exchange undoubtedly occurred, the particular combination of temperature and H isotopic composition of the injected fluid used during CSS appears to have yielded post-steam δ2H values that are indistinguishable from pre-steam values. Only samples from near-injector core G-OB3 that contain hydroxy-interlayered smectite have lower δ2H values as a result of CSS.

The Inner Mongolian Plateau lies along the northern limit reached by the East Asian summer monsoon. This geographic setting makes it especially sensitive to environmental change and an excellent site for understanding Quaternary East Asian monsoon variability. In this study we present new results of hydrogen isotopic compositions of fatty acids extracted from sediments, which were used to construct Holocene paleoprecipitation (or moisture) changes in Northern China. The hydrogen isotopic composition (D/H ratio) of n-acids in the sedimentary sequence of the Duoerji peat, Inner Mongolia, was determined with gas chromatography and mass spectrometry. Changes in the precipitation from middle Inner Mongolia are recorded by the D/H ratio of n-C20, n-C22, n-C24, n-C26, n-C28 acids (δD). From 10–9 ka, the relatively high δD values indicate reduced precipitation in the Early Holocene. Subsequently, increased precipitation is reflected by reduced δD values from 9–5.5 ka. After 5.5 ka, gradually increasing δD values record an overall decrease in precipitation. The precipitation trends established for the Duoerji sequence are consistent with other major paleoclimate proxies in the East Asian monsoon region, especially with a distinct Holocene optimum of increased monsoonal activity from 9–5.5 ka. The δD resulting paleo-precipitation record clearly shows that the Holocene climate in Northern China is basically controlled by the insolation changes.

In situ microanalysis of solid samples is often performed using secondary ion mass spectrometry (SIMS) with a submicron ion probe. The destructive nature of the method makes it mandatory to prevent information loss by using instruments combining efficient collection of secondary ions and a mass spectrometer with parallel detection capabilities. The NanoSIMS meets those requirements with a magnetic spectrometer but its mass selectivity has to be improved for accessing opportunities expected from polyatomic secondary ions. We show here that it is possible to perform D/H ratio measurement images using 12CD−/12CH−, 16OD−/16OH−, or 12C2D−/12C2H− ratios. These polyatomic species allow simultaneous recording of D/H ratios and isotopic compositions of heavier elements like 15N/14N (via 12C15N−/12C14N−) and they provide a powerful tool to select the phase of interest (e.g., mineral versus organics). We present high mass resolution spectra and an example of isotopic imaging where D/H ratios were obtained via the 12C2D−/12C2H− ratio with 12C2D− free from neighboring mass interferences. Using an advanced mass resolution protocol, a “conventional” mass resolving power of 25,000 can be achieved. Those results open many perspectives for isotopic imaging at a fine scale in biology, material science, geochemistry, and cosmochemistry.