The phrase "at a key source" is correct and usable in written English.
It can be used when referring to an important or significant origin of information, data, or resources.
Example: "The researchers found valuable insights at a key source that contributed to their findings."
Alternatives: "from a crucial source" or "at a vital source".
In his closing remarks counsel to the inquiry, Tom Kark QC, highlighted the lack of clinical engagement both within the hospital and the wider NHS as a key source of the problems at Mid Staffordshire.
Al-Ḥudaydah served as a key source of revenue for the Ḥūthīs, who received millions of dollars by taxing cargo at its ports.
The amount of customer assets at the firm, a key source of recurring revenue, rose 12percentt in the quarter to $423 billion.
Tuesday's bombing, by contrast, seemed directly aimed at foreign tourists, a key source of income for Turkey.
This could mean that they are the main focal point of the attack, such Olivier Giroud at Arsenal or Harry Kane at Tottenham or they are a key source of creativity such as Silva at Manchester City or Cesc Fabregas at Chelsea.
The VOA's Chinese-language broadcasts at the time were a key source of information for student demonstrators, The Washington Post reported in 1986, relying on VOA news programs for information about their own demonstrations and about similar protests in other Chinese cities.
In this role he raised the alarm about Sabra and Shatilla, and was a key source at the subsequent inquiry into the massacre.
Spatial variability in nutrient and water presence at the field-scale is a key source of uncertainty when quantifying nutrient cycling and water movement in an agricultural system.
Corinne Lamb, Rick and Darien's elder daughter, earned her doctorate in Physics & Astronomy at Johns Hopkins, and has always been a key source of passion for the beauty of space and the night sky in his family.
