The phrase "a thorough mastery of" is correct and usable in written English.
It can be used when discussing someone's deep understanding or expertise in a particular subject or skill.
Example: "To excel in this field, one must have a thorough mastery of the fundamental principles."
Alternatives: "a deep understanding of" or "an extensive knowledge of".
Some 40% of those surveyed demonstrated a thorough mastery of the issues connected with the introduction of the new currency, an increase of 8% on the previous month.
Deftly handling conversational and argumentative exchanges and rude, abrasive outbursts, String Noise demonstrated a thorough mastery of Mr. Zorn's hermetic logic and irresistible whimsy.
It wasn't always clear whom Clinton was defending; because Hillary's voice in her husband's Administration was both strong and unofficial, sorting out the credit and the blame can, at times, require a thorough mastery of nineties-era minutiae.
Partly of Eskimo descent himself, and equipped with a thorough mastery of the Eskimo language, Rasmussen wintered among the most northerly tribe in the world, the Polar Eskimo of northwestern Greenland (1902 04).
The late 15th and early 16th centuries are mainly associated in Italy with the name of Guglielmo de Marcillat (1467 1529), a Frenchman whose works display a thorough mastery of technique.
Besides his thorough mastery of these woodwinds, he introduced an unprecedented range of unique expressive techniques on them.
That, I think, is what we should start noting in Wheeldon's work, his thorough mastery of the ballet technique and his willingness, much of the time, to let the steps carry the meaning.
But as he took requests written on slips of paper filled out by audience members, it became evident that familiarity is not synonymous with thorough mastery.
And that's in addition a love for the written word, copy-editing mastery and a thorough understanding of AP style!
