Resurgent cauldrons are defined as cauldrons (calderas) in which the cauldron block, following subsidence, has been uplifted, usually in the form of a structural dome. Seven of the best known resurgent cauldrons are: Valles, Toba, Creede, San Juan, Silverton, Lake City, and Timber Mountain. Geologic summaries of these and Long Valley, California, a probable resurgent caldera, are presented. Using the Valles caldera as a model, but augmented by information from other cauldrons, seven stages of volcanic, structural, sedimentary, and plutonic events are recognized in the development of resurgent cauldrons. They are: (I) Regional tumescence and generation of ring fractures; (II) Caldera-forming eruptions; (III) Caldera collapse; (IV) Preresurgence volcanism and sedimentation; (V) Resurgent doming; (VI) Major ring-fracture volcanism; (VII) Terminal solfatara and hot-spring activity. These stages define the terminal cycle of resurgent cauldrons, which in the Valles caldera spanned more than 1 million years. The known and inferred occurrence of the seven stages in the eight cauldrons discussed, together with some time control in four cauldrons, indicates that resurgent doming is early in the postcollapse history; hence, it seems part of a pattern and not fortuitous. Doming of the cauldron block by magma pressure is preferred to doming by stock or laccolithic intrusion, although these processes may be subsidiary. Magma rise that produces doming may be explained in several ways, but the principal cause is not known. Nor is it known why some otherwise similar calderas do not have resurgent domes, although size and thickness of the cauldron block and the degree to which it was deformed during caldera collapse may be factors. All known resurgent structures are larger than 8 miles in diameter and are associated with silicic and, presumably, high-viscosity magmas. Genetically, resurgent cauldrons belong to a cauldron group in which subsidence of a central mass takes place along ring fractures and is related to eruption of voluminous ash flows, thereby differing from Kilauean-type calderas. It is proposed that typical Krakatoan-type calderas differ in that collapse is chaotic and ring fractures are not essential to their formation. Krakatoan calderas typically occur in the andesitic volcanoes of island arcs or the eugeosynclinal environment, and their sub-volcanic analogues are not known, whereas resurgent and related Glen Coe-type cauldrons are more common in cratonic or post-orogenic environments as are their sub-volcanic analogues — granitic ring complexes. Granitic ring complexes, such as Lirue, Sande, Ossipee, and Alnsjø, are probably the closest sub-volcanic analogues of resurgent calderas. The source areas of most of the ash-flow sheets of western United States and Mexico are yet to be found. It is suggested that many of them will prove to be resurgent structures. Present evidence suggests that ore deposits are more commonly associated with resurgent cauldrons than with other cauldron types.

Abstract The midcontinent of the United States hosts some of the world's largest, economically most valuable mineral districts and metallogenic provinces. The Precambrian iron deposits of the Lake Superior region include both Algoma- and Lake Superior-type Fe and Fe-Mn ores. Native cu and Cu-Ni sulfides occur in the mafic igneous rocks of the Keweenawan rift, and in the Late Precambrian Nonesuch Shale. The largest Au producer in the Western Hemisphere, the Homestake Mine in the Black Hills, yields its gold from cummingtonite schist, a metamorphosed iron-carbonate formation. (The most famous ores of this region, however, are not Precambrian; they are the Mississippi-Valley type Pb, Zn, fluorite, and barite deposits in the Paleozoic platform carbonates.) The Middle Proterozoic Fe-cu-REE metallogenic province of the st. Francois terrane, although not as large as the aforementioned districts, is a unique and interesting metal province and has the potential for new discoveries. The ores may be variants of the Kiruna- and Olympic Dam-type class of deposits. The St. Francois Mountains constitute the exposed part of an extensive anorogenic terrane of granite ring complexes and associated rhyolites that underlie most of southeastern Missouri. This igneous terrane is characterized by the predominance of silicic over mafic rocks and by alkalic-intermediate rocks (trachytes), and is not metamorphosed. Its distinctive ore deposits include volcanic-hosted magnetite-hematite-apatite (e.g., Pea Ridge, Pilot Knob); hypo-xenothermal vein deposits of W, Ag, and Pb (Silver Mine district); and vein and replacement deposits of Mn. The Precambrian terrane of the St. Francois Mountains has been deeply eroded and dissected, resulting in a rugged topography and the unroofing of granite. Upper Cambrian marine sedimentary rocks are in nonconformable contact with the underlying igneous rocks. Near the crest of the Ozark dome, the dominant structural feature, the Precambrian outcrops of the ;St. Francois Mountains represent a structural and topographic high. The granite ring complexes correspond to the deeply eroded roots of a formerly more extensive volcanic terrane comprising several calderas, cauldron subsidence structures, ring intrusions, and resurgent cauldrons with central plutons (Kisvarsanyi, 1981). The outcrops of the Precambrian rocks, the network of major roads in the St. Francois Mountains, and the scheduled field trip stops are shown in Fig. 1. The Precambrian rock units compiled by Pratt et al. (1979) and Kisvarsanyi (1981) are shown in Table 1. The volcanic superstructure of the st. Francois terrane has been largely removed by pre-Paleozoic erosion, but as much

Abstract Ohmoto (1977a and b, 1978) suggested that explosive felsic volcanism during the Nishikurosawa stage created submarine calderas and that Kuroko mineralization occurred in marginal depressions (moat areas) of the calderas. His suggestions were based largely on the realization that. all Kuroko deposits formed after the eruption of a large volume of T 4 and T 3 tuffs, that normal faults with vertical displacements of more than 100m were common during T 3 tuff eruptions, and that several phases of resurgent and subsident activity were suggested from changes in the assemblages of benthic foraminifera. The exact geometry of the submarine calderas—whether the Hokuroku basin represented a large single caldera or a composite of several smaller calderas—was not certain at that time. Following the suggestions by Ohmoto (1977b), Kouda and Koide (1978) examined the distribution of post-Kuroko intrusive rocks (dacites and quartz-diorites); they recognized several ring strUctures 3 to 10 km in diameter in the Hokuroku district and suggested that the Kuroko and vein deposits formed in the marginal zones of resurgent cauldrons indicated by these ring structures. Ring structures, alone, however, are not sufficient evidence for calderas or for relating calderas to ore, genesis. Additional evidence may be found, however, from an examination of the spatial distributions of not only the prnit-Kuroko felsic intrusives (dacites D 2 , D 1 , D 0 , and quartz-diorite) but also of the pre-Kuroko dacites (D 4 ), post-Kuroko basalts and dolerites (B 2 and B 1 ), pre-, syn-, and post-Kuroko tuffs and tuff breccias (T 4 , T 3 and T 2 ), and syn- and postKurokomudstones (M 2 ). Data used

Abstract The Emory cauldron is traversed by New Mexico 90 about 35 mi (55 km) east of Silver City, in southwestern New Mexico.