Barite is an abundant sulfate mineral in nature. Especially, the variety of morphologies of barite is often driven by the mixing of Ba-bearing hydrothermal fluid and sulfate-bearing seawater around hydrothermal chimneys. In order to better understand the factors affecting the morphology and precipitation mechanism(s) of barite in seafloor hydrothermal systems, we synthesized barite by a new method of in-situ mixing of BaCl₂ and Na₂SO₄ solutions at 200 °C while varying Ba concentrations and ratios of Ba²⁺/SO₄²⁻, and at room temperature for comparison. The results show that barite synthesized by in-situ mixing of BaCl₂ and Na₂SO₄ solutions at 200 °C forms a variety of morphologies, including rod-shaped, granular, plate-shaped, dendritic, X-shaped, and T-shaped morphologies, while room temperature barites display relatively simple, granular, or leaf-like morphologies. Thus, temperature affects barite morphology. Moreover, dendritic barite crystals only occurred at conditions where Ba²⁺ is in excess of SO₄²⁻ at the experimental concentrations. The dendritic morphology of barite may be an important typomorphic feature of barite formed in high-temperature fluids directly mixing with excess Ba²⁺ relative to SO₄²⁻.

The dissolution of dolomite can not only provide the chemical components in hot springs but also provide a high-quality reservoir for geothermal resources. However, there is still debate about the main controlling factors and mechanisms of the dissolution process of dolomite. The Shuijing hot springs in Guizhou Province are rich in SO₄²⁻ and the geothermal reservoir is dolomite, which provides an excellent opportunity to understand the role of SO₄²⁻ in the dissolution process of dolomite. In this paper, water–rock interaction experiments were conducted at different temperatures to study the effects of SO₄²⁻, pH, and CO₂ on the dissolution of dolomite from the Shuijing hot springs geothermal reservoir. The results indicate that temperature is a significant factor affecting the chemical composition of hot springs water, with higher temperatures having a more pronounced effect on the dissolution of dolomite. At lower temperatures of 25 °C and 90 °C, the molar ratio of the released Ca²⁺ and Mg²⁺ during the dissolution of dolomite in the initial reaction stage generally approaches the Ca/Mg molar ratio of dolomite, exhibiting congruent dissolution. However, at elevated temperatures of 150 °C, the released Ca/Mg molar ratio surpasses the Ca/Mg molar ratio of dolomite, demonstrating an incongruent dissolution characteristic with Ca²⁺ being preferentially released over Mg²⁺. Additionally, the relative importance of CO₂, SO₄²⁻ and pH on the dissolution degree of dolomite is CO₂ > SO₄²⁻ > pH = 4 > pH = 7 > pH = 10. The promotion effect of SO₄²⁻ on dolomite dissolution indicates that the greater the SO₄²⁻ concentration, the stronger the dissolution of dolomite, and its dissolution ability is enhanced with the increase in temperature. Furthermore, the effect of CO₂ on the dissolution of dolomite is stronger than that of SO₄²⁻, leading to the oscillating fluctuation trend of the released Ca²⁺ and Mg²⁺.