The phrase "vast mix" is grammatically correct and can be used in written English.
It is often used to describe a large and diverse combination of things or elements. Example: "The city's cultural scene is a vast mix of art, music, theater, and cuisine from all around the world."
Several promising new developments are sprouting downtown, most notably a vast mixed-use center on the site of a former steel plant.
Schools and libraries were followed by two 32-storey apartment towers of Corbusian dimensions in Belo Horizonte, called Governor Kubitschek Buildings, but even these would have been outdone by a vast mixed-use building planned for the city of Petropolis which, had it been built, would have been a quarter of a mile long, with 5,700 apartments, shops, offices and hotels.
People who had bought ball clubs because they loved the game or because ownership satisfied their need for status and recognition suddenly found themselves not in sports but in entertainment, competing not merely with each other but with all the other elements in that vast gaudy mix known as American popular culture.
Dedicating an astronomic budget, the company uses vast marketing mix to communicate this giant sponsorship.
A key informant talked about this staffing mix in both positive and negative terms: We do have a vast mixture of personnel looking after the mothers.
He created a vast mythology, mixing Biblical elements with prophetic figures of his own, and stirred in experiences from his own life too.
The Brooklyn I know is a vast socio-economic mix.
Going for the pound shop vibe that has swamped the high street, shelves are packed high with a vast and eclectic mix of goods.
Their base, Teesdale, lies in the Durham Dales, a vast and scenic mix of long open views where communities were previously involved across centuries of mining – first with lead then coal.
