A revised age, structural model and origin for the North Pennine Orefield in the Alston Block, northern England: intrusion (Whin Sill)-related base metal (Cu–Pb–Zn–F) mineralization

Abstract

Mineralization and associated fluid migration events in the ca 1500 km2 North Pennine Orefield (NPO) are known to be associated with tectonic activity, but the age of these tectonic events and origins of the base metal sulphide mineralization remain unresolved. New fieldwork in the Alston Block shows that mineralization post-dates a weakly developed phase of N-S shortening consistent with far-field Variscan basin inversion during the late Carboniferous. New observations of field relationships, coupled with microstructural observations and stress inversion analyses, together with Re-Os sulphide geochronology show that the vein-hosted mineralization (apart from barium minerals) was synchronous with a phase of N-S extension and E-W shortening coeval with emplacement of the Whin Sill (ca 297-294 Ma). Thus the development of the NPO was related to an early Permian regional phase of transtensional deformation, mantle-sourced hydrothermal mineralization and magmatism in northern Britain. Previously proposed Mississippi Valley Type models, or alternatives relating mineralization to the influx of Mesozoic brines can no longer be applied to the development of the NPO in the Alston Block. Our findings also mean that existing models for equivalent base metal sulphide fields worldwide (e.g. Zn-Pb Districts of Silesia, Poland and Tennessee, USA) may need to be reassessed.

First Evidence of the Post-Variscan Magmatic Pulse on the Western Edge of East European Craton: U-Pb Geochronology and Geochemistry of the Dolerite in the Lublin Podlasie Basin, Eastern Poland

“…The impact of contamination is demonstrated by significant similarity of the Mielnik IG and UCC patterns on multielement diagram normalized to PM (Figure 10B). It is the contrast to the most of the Tajno rocks including coeval (300 Ma) camptonite, that plot in the depleted mantle quadrant of the Nd-Sr correlation diagram (Figure 12B) with low 87 Sr/ 86 Sr ratios and positive ENd (t) . The higher values of 87 Sr/ 86 Sr ratios = 0.70940 and strong negative ENd (300) = −9.75 obtained in Mielnik IG1, and that plot in the enriched mantle quadrant, rather exclude the same source and the petrogenetic connection with early Carboniferous Tajno suite.…”

“…It is the contrast to the most of the Tajno rocks including coeval (300 Ma) camptonite, that plot in the depleted mantle quadrant of the Nd-Sr correlation diagram (Figure 12B) with low 87 Sr/ 86 Sr ratios and positive ENd (t) . The higher values of 87 Sr/ 86 Sr ratios = 0.70940 and strong negative ENd (300) = −9.75 obtained in Mielnik IG1, and that plot in the enriched mantle quadrant, rather exclude the same source and the petrogenetic connection with early Carboniferous Tajno suite. Most likely the dolerite remains a more individual response to the regionally intensified extension.…”

“…A similar conclusion can be drawn from the compilation of previously obtained isotope data (Figure 12). [9,86], data from Tajno alkaline ultramafic suite [30,87] and Mielnik dolerite dyke (recalculated after age revision) and Late Neoproterozoic dolerite of the Volyn igneous province [25,88] The mantle components DMM (depleted MORB mantle), PREMA (prevalent mantle), and EM I (enriched mantle, type I) are taken from [89], EM II (enriched mantle, type II) from [90].…”

“…The comparison of published Nd and Sr isotope ratios from a few Carboniferous intrusions collected in Figure 12 shows an individual character of the Mielnik IG1 dolerite. This compilation includes data from Scania dolerites [9]), Whin Sill of Northern England [86] together with data from TTZ margin of the EEC with distinct ultramafic−alkaline to carbonatite rocks of the Tajno massif [30,87] and the dolerites from the Volyn province and recalculated result of the Mielnik IG1 dolerite [25,88]. The variations in 143 Nd/ 144 Nd (Figure 12A) demonstrate at least two separate type of sources.…”

“…The variations in 143 Nd/ 144 Nd (Figure 12A) demonstrate at least two separate type of sources. The low value of 143 Nd/ 144 Nd of the Mielnik IG1 sample is undoubtedly related to the contamination of its 143 Nd/ 144 Nd (0) ratio against 147 Sm/ 144 Nd ratio and (B) ENd (t) against 87Sr/86Sr, including the Carboniferous/Permian dyke swarms from Scania, Whin Sill of Northern England [9,86], data from Tajno alkaline ultramafic suite [30,87] and Mielnik dolerite dyke (recalculated after age revision) and Late Neoproterozoic dolerite of the Volyn igneous province [25,88] The mantle components DMM (depleted MORB mantle), PREMA (prevalent mantle), and EM I (enriched mantle, type I) are taken from [89], EM II (enriched mantle, type II) from [90].…”