Abstract The palaeotemperature recorded by vitrinite reflectance ( R o ) in the pre-Cenozoic uplifted stratigraphic strata, and in Palaeozoic–Mesozoic remnant basins outside the Cenozoic depocentres, has not been overprinted by later thermal events in the eastern North China Craton (NCC). Based on downhole R o data from the Palaeozoic and the Mesozoic subsections, we reconstruct the temperature gradients when the subsections reached their maximum palaeotemperatures in the Middle Triassic and the Cretaceous, and calculate the corresponding heat flow histories since the early Mesozoic. The temperature gradient and heat flow were much higher in the Cretaceous (35–43 °C km −1 and 73–83 mW m −2 , respectively) than in the Middle Triassic and at the present. The high palaeo-heat flow during the Late Mesozoic implies that the thickness of the ‘thermal’ lithosphere at that time was c . 65 km, about half the thickness of c . 135 km estimated for the Early Mesozoic. The change from a stable thermal regime to an active thermal regime took place during the Late Jurassic–Early Cretaceous ( c . 110 Ma). This tectonothermal event was accompanied by extensive surface erosion, and is also evidenced in the areas adjacent to the NCC, such as the South Yellow Sea and East China Sea basins. Our study provides not only geothermal evidence for the Late Mesozoic lithospheric thinning, but also additional constraints on the thinning mechanism, which is currently being debated.

Abstract Gold mineralization at the Victory mine, Kambalda, is associated with discrete metasomatic alteration zones around quartz breccia zones, shear zones, and quartz vein arrays. The mineralogy, textures, and whole-rock chemistry of the wall-rock alteration zones are described for several different host rocks. Mineral assemblages at zone boundaries, calcite-dolomite geothermometry, and amphibole geobarometry have been used to estimate the temperature, pressure, and fluid composition associated with metasomatism. Fluid inclusion data have been used to estimate independently these conditions. Wall-rock alteration zones extend up to 3 m from veins and breccias at the Victory mine. Textures indicate that the zoned wall-rock alteration and associated gold mineralization postdated regional metamorphism and outlasted retrograde carbonation. Chemical variations across zoned alteration profiles indicate that alteration occurred at approximately constant volume. Outer alteration zones are characterized by the addition or loss of H 2 O, CO 2 , Na, and K whereas Al, Mg, Ca, Fe +2 , and Fe +a were mobile in the inner alteration zones. Chemical changes and mineralogy of the alteration envelopes depended critically on the initial composition of the host rock which affected the resultant mineral assemblages. Assuming that local equilibrium conditions existed at alteration zone boundaries, mineral compositions from microprobe data have been used to model equilibria in the system SiO 2 -Al 2 O 3 -MgO-CaO-K 2 O-H 2 O-CO 2 . The mineral equilibria together with calcite-dolomite geothermometry provide an estimate of 390° ± 40°C for metasomatism which is similar to a minimum temperature estimate of 370° + 30°C from fluid inclusion data. Mineral equilibria and fluid inclusion data suggest that pressure during metasomatism was approximately 1.7 to 2 kbars. Fluid inclusion data indicate that metasomatism was associated with a homogenous H 2 O-CO 2 -NaCl fluid containing 19 to 36 wt percent CO 2 CX CO2 = 0.1-0.2) and 8 to 9 equiv wt percent NaCl. The data presented in this study indicate that metasomatism occurred at considerably lower temperatures and pressures than those estimated for peak metamorphic conditions at Victory. Thus after peak metamorphism, substantial uplift occurred before the hydrothermal emplacement of gold.