Hydrothermal fluids played a key role in establishing the environmental conditions in which ancient stromatolites grew within the North Pole Chert of the ~3.48 Ga Dresser Formation (Pilbara Craton, Western Australia). However, there has been uncertainty as to the physicochemical conditions of the hydrothermal system in relation to (i) the distribution of hydrothermal alteration, (ii) the relative contribution of seawater and/or magmatic volatiles to the hydrothermal fluids, and (iii) the origin of some of the major elements mobilized in the hydrothermal fluids.

This study examines the hydrothermal alteration of the underlying North Star Basalt in order to better understand the nature of the circulating fluids and to determine the processes responsible for the transport and accumulation of metals and metalloids to the near surface environment. Detailed geological mapping reveals a complex distribution of alteration mineral assemblages that is controlled at all stratigraphic depths by the distance to the major fluid pathways that are now represented by hydrothermal silica veins. With increasing distance from the vein margins, alteration assemblages change from argillic (kaolinite–quartz) to phyllic (illite–quartz), and then to propylitic (chlorite–albite–epidote) and actinolitic (actinolite–albite–chlorite–epidote) at more distal positions. Illite Ar–Ar dating of argillic–altered basalt proximal to major hydrothermal veins immediately below the North Pole Chert confirms a syn–depositional hydrothermal origin of alteration, and demonstrates that the mineralogical and chemical features developed through the circulation of hydrothermal fluids were largely preserved after subsequent thermal overprints at 3.25, 3.06, and 2.29 Ga.

The spatial distribution of the alteration mineral assemblages indicates that the fluids circulating in the hydrothermal system were highly acidic (pH < 3) for at least some time during the evolution of the Dresser Caldera. Such highly acidic fluid conditions were likely promoted by the input of magmatic volatile phases, such as HCl, SO₂, H₂S, and F. Bulk geochemical analyses of altered basalts reveal that large amount of metals, including Fe, Mg, Ni, and Zn, were leached from the North Star Basalt during hydrothermal alteration and delivered to the surface. Furthermore, our data indicate that K and Ba were introduced into the hydrothermal system from external reservoir(s). Although the contribution of K–rich seawater cannot be completely discounted, we argue that the bulk of K and Ba was sourced from an underlying magma chamber undergoing fractional crystallization of a melt with TTG–like composition.

热液流体在建立古代叠层石在 ~3.48 Ga Dresser 地层（西澳大利亚皮尔巴拉克拉通）的北极燧石内生长的环境条件方面发挥了关键作用。然而，与 (i) 热液蚀变的分布，(ii) 海水和/或岩浆挥发物对热液流体的相对贡献，以及 (iii)热液中流动的一些主要元素的起源。

这项研究检查了下伏北极星玄武岩的热液蚀变，以更好地了解循环流体的性质，并确定负责金属和准金属向近地表环境运输和积累的过程。详细的地质绘图揭示了蚀变矿物组合的复杂分布，其在所有地层深度都受到与现在以热液二氧化硅脉为代表的主要流体通道的距离的控制。随着距脉缘距离的增加，蚀变组合由泥质（高岭石-石英）转变为页岩（伊利石-石英），再转变为青石质（绿泥石-钠长石-绿帘石）和阳起石（阳起石-钠长石-绿泥石-绿帘石）远端位置。

蚀变矿物组合的空间分布表明，在德莱赛火山口演化过程中，热液系统中循环的流体至少在一段时间内呈高酸性（pH < 3）。这种高酸性流体条件可能是由岩浆挥发相的输入促进的，例如 HCl、SO ₂、H ₂S 和 F。对蚀变玄武岩的大块地球化学分析表明，大量金属，包括 Fe、Mg、Ni 和 Zn，在热液蚀变过程中从北极星玄武岩中浸出并输送到地表。此外，我们的数据表明 K 和 Ba 是从外部储层引入热液系统的。尽管不能完全忽视富含钾的海水的贡献，但我们认为大部分 K 和 Ba 来自底层岩浆房，该岩浆房经历了类似 TTG 成分的熔体的分步结晶。