ABSTRACT Mississippian (Tournaisian–Viséan) carbonate mounds in the Compton and Pierson limestones, Ozark region, North America, have been called Waulsortian. However, European Waulsortian mounds contain features such as geopetals with multigenerations of carbonate mud (polymuds) and stromatactis cavity systems that are rare to absent in Ozark mounds. To determine similarities and differences, examine their origins, and clarify nomenclature, mounds in the Compton and Pierson limestones are compared with Waulsortian mounds in the Feltrim Limestone, Ireland. Features considered included mound size, geometry, style of aggradation, composition, depositional setting, and diagenetic history. Mounds in the Compton and Pierson limestones are <10 m (33 ft) thick and form singular knoll-form or aggregates with a strong lateral growth component. In contrast, individual Waulsortian mounds in the Feltrim Limestone range from 5 to > 30 m ( 16 – 100 ft ) thick, but coalesce and vertically aggrade to form complexes that exceed 500 m ( 1600 ft ) . Pierson mounds are crinoidal and grain-rich, whereas Compton and Feltrim mounds are bryozoan-rich and mud-dominated. All mounds have similar cement stratigraphy and diagenetic histories. Mud-rich Compton mounds and Feltrim mounds are interpreted as deeper water than skeletal-rich Pierson mounds. Limited accommodation constrained Compton and Pierson mound size and forced lateral aggradation. Subsidence-driven accommodation in the Dublin Basin allowed Feltrim mounds to grow larger, coalesce, and aggrade vertically. Three types of mounds are recognized: true Waulsortian in the Feltrim Limestone, mud-cored Waulsortian-type Compton and Pierson mounds, and Pierson transported bioaccumulation mounds. Small dimensions of Waulsortian-type Pierson and Compton mounds limit their potential as oil and gas reservoirs, whereas Pierson crinoidal sediment piles are known to form reservoir-size accumulations.

Abstract In the first decade of the 21 st century, surface exploration drilling around the Boliden Tara mine at Navan, Ireland, aimed at ~1-km-deep targets, was becoming ineffective. During 2010, the extensive geologic knowledge of the existing Navan orebody was leveraged in an Experts Meeting to promote near-mine discovery. Two ideas, of many, were of relevance to this paper: (1) undiscovered mineralized fault-related zones were predicted south of the orebody, and (2) seismic surveys could locate subsurface faults. By late 2012, seven 2D seismic lines (totaling 101 km) had been acquired, processed, and initially interpreted. Pre-stack time migration images were used for interpretation, augmented by diamond drill core data where available. The seismic imaging proved a “game changer” in terms of subsurface visualization and a priority target was identified 2 km south of the mine on the footwall crest of a large south-dipping basin-margin fault. The first hole intersected 34 m of mineralized rock with 14% Zn + Pb, but at greater depth than anticipated. Follow-up drilling was initially successful but proved to be challenging. The first hole intersected a deep structurally complex section of the newly discovered zone that required more drilling to establish its location and attitude. Further drilling, utilizing extensive navigational deflection technology, outlined a mineralized zone similar in nature to the Navan 5 Lens at depths of 1 to 2 km. Inferred resources through 2016 were estimated at 10.2 Mt grading 8.5% Zn and 1.8% Pb. Underground exploration development of this zone commenced in April 2017, and will allow accurate delineation of this significant discovery.