How does radium-226 occur naturally in uranium ores?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — alkaline-earth metal Modern version of the periodic table of the elements (printable).

Radium-226 occurs naturally in uranium ores as a result of the continuous radioactive decay of uranium-238. Because all isotopes of radium are radioactive and relatively short-lived on a geological time scale, any primeval radium has long since disappeared; therefore, it exists today only as a disintegration product within natural radioactive decay series.1

Specifically, radium-226 is a member of the uranium-decay series. In this process, it is formed from its parent isotope, thorium-230, and subsequently decays into radon-222. While radium is present in all uranium ores, it is widely distributed in nature because it can form water-soluble compounds.1