As a continuation of the investigations of hydrothermal activity on sediment covered ridge axes begun in the Gulf of California (Guaymas Basin), support is provided for a diving expedition to the Gorda Ridge in the Northeast Pacific. The southern end of this slow spreading ridge (Escanaba Trough; half- rate (12 mm/yr) is buried under several hundred meters of turbidite sediments derived from the mountainous coasts of the Pacific Northwest. The sediment composition, immature sands of metamorphic and granitic origin, contrasts sharply with the mixture of andesitic and biogenic debris encountered in Guaymas. The hydrothermal system is thus an extreme end-member with only three components: seawater, tholeiites, turbidites and as a result, the contribution of the sediment to the chemistry of the hydrothermal fluids will be easy to discern. This is especially true since the sediment- starved northern part of the Ridge is also available for study. In a comparative study of these two systems it will be possible to establish the effectiveness of reactions with purely detrital sediments in localizing ore deposits and in controlling their chemistry.//
