Abstract A new genetic model is proposed for the formation of the St Austell kaolin deposits, incorporating geological, isotopic, paragenetic and microthermometric evidence from kaolin-quartz veins combined with a reconstruction of the thermal evolution of the Cornubian pluton during the Mesozoic. Fluid inclusions in quartz, paragenetically associated with kaolin, document that the kaolinization took place at temperatures between 50 °C and 100 °C, indicating that the kaolinization is a low-temperature hydrothermal event coincident with the oil generation window. Kaolinization occurred prior to the unroofing of the pluton, during the Late Jurassic to Early Cretaceous. The kaolinization is thus contemporary with the major Early Cretaceous uplift that affected the Cornubian massif as a consequence of rifting in the offshore Western Approaches. Geological, isotopic and geochemical considerations argue strongly against the involvement of unmodified meteoric waters in the kaolinization process. The most plausible fluid types for the kaolinization are either basinal brines expelled from Permo-Triassic sediments of the adjacent offshore Plymouth Basin, or highly evolved meteoric waters that circulated through the sediments enclosing the pluton. The kaolinization process converted large volumes of fractured granite to a porous quartz kaolin rock matrix.

Abstract The chemical composition of sea water is practically constant in all parts of the ocean except for elements that are present in small quantity and which are needed for the growth of organisms. Life in the sea depends mainly upon the development of the microscopic plants, or the phytoplankton, as they are called. The phytoplankton develops in the upper 100 meters of water where sun-light is effective, as long as certain mineral nutrients, such as nitrates, phosphates, silicates, and iron compounds, are present above certain minimum quantities. If the amount of any of one of the inorganic requisite foods for the phytoplankton drops below the particular minimum, the growth of phytoplankton ceases and no more phytoplankton develops until the essential nutrients have been replenished. Organisms when they die are decomposed by bacteria and the mineral substances that they contain and which are essential for plant life are returned to the sea again, mostly below the zone of photosynthesis. If this subsurface water rich in nutrients is raised to the surface by turbulence, convection, or currents the phytoplankton begins to grow again. The phytoplankton removes carbon dioxide from the surface layers of water, thus tending to make them over-saturated with respect to calcium carbonate. Below the zone of photosynthesis, decomposing organic matter gives off carbon dioxide to the water, which tends to make the deep water undersaturated with calcium carbonate. Organisms in the sea contain a larger percentage of metals, such as copper, zinc, arsenic, and even gold and silver, than does the water itself. Some of these metals are needed for the metabolic process of the organisms, others are adsorbed on the surface of the organisms. (Editor’s abstract.)

Abstract The chemical composition of sea water is practically constant in all parts of the ocean except for elements that are present in small quantity and which are needed for the growth of organisms. Life in the sea depends mainly upon the development of the microscopic plants, or the phytoplankton, as they are called. The phytoplankton develops in the upper 100 meters of water where sun-light is effective, as long as certain mineral nutrients, such as nitrates, phosphates, silicates, and iron compounds, are present above certain minimum quantities. If the amount of any of one of the inorganic requisite foods for the phytoplankton drops below the particular minimum, the growth of phytoplankton ceases and no more phytoplankton develops until the essential nutrients have been replenished. Organisms when they die are decomposed by bacteria and the mineral substances that they contain and which are essential for plant life are returned to the sea again, mostly below the zone of photosynthesis. If this subsurface water rich in nutrients is raised to the surface by turbulence, convection, or currents the phytoplankton begins to grow again. The phytoplankton removes carbon dioxide from the surface layers of water, thus tending to make them over-saturated with respect to calcium carbonate. Below the zone of photosynthesis, decomposing organic matter gives off carbon dioxide to the water, which tends to make the deep water undersaturated with calcium carbonate. Organisms in the sea contain a larger percentage of metals, such as copper, zinc, arsenic, and even gold and silver, than does the water itself. Some of these metals are needed for the metabolic process of the organisms, others are adsorbed on the surface of the organisms. (Editor’s abstract.)